Castrated Animals Research Articles

Immunocastration in cattle and pigs

Abstract Raising gonad-intact farm animals has many advantages over conventional castrates. Intact animals are generally more efficient in the conversion of feed into lean meat. In addition to decreasing production costs, better feed efficiency also leads to a reduction in the output of various biological pollutants, particularly nitrogen. Moreover, traditional surgical castration is perceived by many people to be ethically questionable. However, intact animals tend to cause problems, mostly in terms of management for cattle, mostly in terms of meat quality for pigs. Among the various methods envisaged as alternatives to surgical castration, the present review is focused on active immunisation against gonadotrophin-releasing hormone (GnRH). Pilot studies have demonstrated that, providing a good immune response is achieved, this technique is very efficient in preventing aggressive and sexual behaviour in bulls, oestrus behaviour in heifers and boar taint in male pigs. Performance of the immunocastrated animals are generally intermediates between those of intact and surgically castrated animals. Immunisation against GnRH appears to be a very attractive approach to castration of farm animals. However, these results still need to be confirmed with sufficient animal numbers. In addition, much work remains to be done to try to reduce animal variation in response to active immunisation and to reduce the adverse side effects associated with traditional adjuvants. The problems related to the immunocastration of male pigs should be easier to solve than those for cattle, because only short -term biological responses are required.

Immunocytochemical localization of seminal proteins in salivary and lacrimal glands of the rat.

Antibodies against 10 different secretory proteins from the accessory sex glands of the male rat were used for immunohistochemical studies of salivary and lacrimal glands from intact and castrated rats, at the light- and electron-microscopic levels. In the parotid gland, secretory acinar cells showed immunoreactivity with antibodies against prostatic binding protein, cystatin-related peptide and acid phosphatase (isoenzyme pI 8.0; 5.6) typical of ventral prostate, and seminal vesicle secretion VI. Western blotting analysis indicated that immunoreactivity against prostatic binding protein was attributable to a subunit, presumably C3. Acid phosphatase pI 5.6 showed a molecular weight of 66 kDa, which is at variance with the prostatic form. Immunoreactivity for secretory transglutaminase, derived from the coagulating gland, was restricted to myoepithelial and stromal cells. In castrated animals, the immunoreactivity of acinar cells was reduced to the background level, whereas stromal transglutaminase immunoreactivity was unaltered. The distribution pattern of immunoreactivity for the proteins mentioned was almost identical in the lacrimal gland. Significant differences were however observed in the immunoreactivity of the inframandibular gland, where serous glandular cells were non-immunoreactive for seminal proteins, with the exception of acid phosphatase isoenzyme pI 8.0. Granules present in the convoluted granular ducts were immunoreactive particularly for acid phosphatase (isoenzyme pI 5.6) but much less for cystatin-related peptide; immunoreactivity was reduced after castration. The straight portion of the inframandibular duct system was immunoreactive for transglutaminase, but no influence of castration was visible. The distribution of immunoreactivity for seminal proteins present in the salivary and lacrimal glands and the pronounced androgen-dependence of their expression point to functional relationships of the respective proteins at both glandular sites.

Growth inhibition of human prostate tumor cells by an agonist of gonadotrophin-releasing hormone.

The effect of [D-Leu6,des-Gly-NH2(10),Proethylamide9]-GnRH, leuprolide, was determined for the human primary prostate tumor cell line ALVA-31 by in vitro mitogenic assays. Prostate tumor cell proliferation was inhibited up to 50% by leuprolide. Inhibition was not observed in parallel cultures treated with other low molecular weight bioactive peptides. The incorporation and metabolic reduction of testosterone was not affected by concentrations of leuprolide that were inhibitory in the mitogenic assay. Specific high-affinity binding of 125I-labeled leuprolide was also demonstrated on intact tumor cells with an estimated effective median dose (ED50) of < 1 x 10(-9)M. Inhibition of prostate tumor growth was further demonstrated in Balb/c athymic intact and castrate male mice bearing ALVA-31 tumor xenografts following chronic administration of leuprolide. These data clearly demonstrate that leuprolide can inhibit the growth of a human prostate carcinoma cell line. Studies conducted in castrate animals further suggest an alternative mechanism of growth inhibition that appears to be independent of the suppression of steroid hormone biosynthesis by LHRH analogues.

Estradiol enhances the stimulatory effect of insulin-like growth factor-I (IGF-I) on mammary development and growth hormone-induced IGF-I messenger ribonucleic acid.

Pubertal mammary development in the rat is largely dependent upon GH and estrogen. We recently showed that insulin-like growth factor-I (IGF-I) can substitute for GH in inducing mammary development in male rats, suggesting that IGF-I mediates GH action. The present study investigated whether IGF-I, like GH, required estradiol (E2) to act or whether IGF-I could substitute for both GH and E2. The effects of IGF-I were tested in the presence and absence of E2. Elvax pellets containing IGF-I or des(1-3) IGF-I were implanted into right lumbar mammary glands of sexually immature, hypophysectomized, oophorectomized female rats, with control BSA-containing pellets in the contralateral glands. After 5 days, both lumbar mammary glands were removed and examined in whole mounts for mammary development by counting terminal end buds and alveolar structures. E2, administered in SILASTIC brand capsules, had no independent effect on mammary development. In the absence of E2, des(1-3) IGF-I had a small, but significant, independent effect on mammary development; native IGF-I was ineffective. The addition of E2 significantly enhanced the effects of IGF-I and des(1-3) IGF-I on mammary development, similar to that noted when E2 was given along with GH. We also studied the effects of E2 and/or hGH on mammary gland IGF-I messenger RNA (mRNA) in hypophysectomized castrated male animals. E2 alone did not increase mammary gland IGF-I mRNA concentrations, but E2 enhanced the effect of hGH on IGF-I mRNA by 4- to 6-fold. These studies indicate that IGF-I can have a small independent effect on mammary development, but like GH, E2 is required for a full effect. They also indicate that E2 is capable of synergizing with GH in the production or expression of IGF-I mRNA, and that the action of E2 on mammary development may take place at multiple sites. If locally produced IGF-I does indeed mediate the action of GH in mammary development, then although E2 is capable of enhancing the effect of GH on IGF-I mRNA, its major effect in mammary development occurs after IGF-I is produced.

The Effect of Long‐Term Castration on the Neuronal and Physiological Responses to Acute or Repeated Restraint Stress: Interactions with Opioids and Prostaglandins

Sixty min supine restraint stress induced a marked, but transient, hypothermic response in intact male rats, which tended to recover towards pre-stress levels or slightly overshoot during the later stages of restraint. Castration reduced the initial hypothermia but increased overshoots. Baseline (pre-stress) core temperature was also higher in castrated than intact rats, but the reduction in stress-induced hypothermia was still present even when this difference had been taken into account. The hypothermic response was not altered during the course of 10 sessions of daily repeated restraint in either intact or castrated rats. Castration did not alter cardiac responses to restraint. Both intact and castrated rats showed marked tachycardia during the initial 12 min of restraint, followed by a gradual fall towards baseline values. Repeated restraint accentuated the second phase of the cardiac response, without modifying the initial tachycardia, in both intact and castrated animals. The response of blood corticosterone levels to the first period of restraint was unaltered by castration but the attenuation observed after 10 sessions of stress was more complete in castrated rats. The neuronal c-fos response 60 min after the last of the series of repeated restraints was less in the hypothalamic paraventricular nucleus, medial amygdala, and locus coeruleus compared with that following the first session, but not in the lateral septum or the bed nucleus of the stria terminalis. Castration did not change the c-fos profile following the same number of restraint sessions. Castration depleted completely the vasopressinergic innervation in the lateral septum, diagonal band of Broca and medial amygdala.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood flow and mineral content of the tibia of female and male rats: changes following castration and/or administration of estradiol or testosterone

We studied changes in the local circulation and mineralization of the rat tibia under different experimental conditions. Four experiments were performed on a total of 155 female and male rats: after oophorectomy (OOX) or orchidectomy (ORX), after the administration of estradiol benzoate (EB, Agofollin Depot, 1 mg/rat once a week or 5 mg/kg body weight once every 5 days for 4 weeks), or after the administration of testosterone (T, Agovirin Depot, 25 mg/kg body weight once every 5 days for 4 weeks). We estimated 85Sr-microsphere uptake and blood flow in the tibia, density of the tibia, and ash weight per bone volume unit. The scheme of the experiments was uniform: experiment A—females—controls, OOX, EB, OOX + EB; experiment B—males—controls, ORX, EB, ORX + EB; experiment C—females—controls, OOX, T, OOX + T; experiment D—males—controls, ORX, T, ORX + T. A sham operation was performed on the animals in the uncastrated groups. The results showed that OOX and ORX stimulated the uptake of 85Sr-microspheres and bone blood flow and reduced both bone density and ash weight, whereas T inconstantly and EB constantly reduced 85Sr-microsphere uptake and bone blood flow and increased bone density and ash weight in both sham-operated and castrated animals. The described changes in the bone blood flow and mineral content under the given experimental conditions suggest a relation in the regulations of both processes, a possible association with resorption of bone, and the importance of the circulation of blood in the metabolism of bone tissue.

Blood Flow and Mineral Content of the Tibia of Female and Male Rats: Changes Following Castration and/or Administration of Estradiol or Testosterone

We studied changes in the local circulation and mineralization of the rat tibia under different experimental conditions. Four experiments were performed on a total of 155 female and male rats: after oophorectomy (OOX) or orchidectomy (ORX), after the administration of estradiol benzoate (EB, Agofollin Depot, 1 mg/rat once a week or 5 mg/kg body weight once every 5 days for 4 weeks), or after the administration of testosterone (T, Agovirin Depot, 25 mg/kg body weight once every 5 days for 4 weeks). We estimated 85Sr-microsphere uptake and blood flow in the tibia, density of the tibia, and ash weight per bone volume unit. The scheme of the experiments was uniform: experiment A—females—controls, OOX, EB, OOX + EB; experiment B—males—controls, ORX, EB, ORX + EB; experiment C—females—controls, OOX, T, OOX + T; experiment D—males—controls, ORX, T, ORX + T. A sham operation was performed on the animals in the uncastrated groups. The results showed that OOX and ORX stimulated the uptake of 85Sr-microspheres and bone blood flow and reduced both bone density and ash weight, whereas T inconstantly and EB constantly reduced 85Sr-microsphere uptake and bone blood flow and increased bone density and ash weight in both sham-operated and castrated animals. The described changes in the bone blood flow and mineral content under the given experimental conditions suggest a relation in the regulations of both processes, a possible association with resorption of bone, and the importance of the circulation of blood in the metabolism of bone tissue.

Chronic administration of neuropeptide Y into the lateral ventricle starting at 30 days of life delays sexual maturation in the female rat.

The role of neuropeptide Y (NPY) in the regulation of sexual function is still controversial. Whereas central NPY administration is stimulatory during proestrus in the rat and other species, such administration is inhibitory in castrated animals and we have shown that chronic, central infusion of NPY inhibits both the gonadotropic and somatotropic axis in adult rats. Previous studies have suggested that NPY could be involved in the triggering of the first ovulatory LH surge and a recent report indicated that a single central NPY injection given at 30 days of life could advance sexual maturation. We therefore evaluated the effect of chronic NPY administration on the timing of sexual maturation in the female rat and compared the effects obtained with those induced by a single NPY injection. Constant infusion of NPY (18 micrograms/day) into the lateral ventricle delayed sexual maturation as seen by the absence of vaginal opening, delayed ovarian growth and reduced number of pituitary GnRH receptors. This inhibitory effect was seen as long as NPY was infused. In contrast, a single NPY injection either at 30 days of life or earlier, or repeated single injections between 28 and 31 days of life, did not modify the pace of sexual maturation. Unlike what is observed in adult animals, overall food intake was only minimally increased between 30 and 37 days of life in chronically NPY-infused rats, but this increase became more important thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of dehydroepiandrosterone (DHEA) on GnRH gene expression in the rat brain as studied by in situ hybridization.

Dehydroepiandrosterone (DHEA) is an adrenal androgen that is converted into potent androgens and/or estrogens in peripheral tissues. To further investigate the potential role of DHEA in reproductive functions in the rat, we have studied the effect of 2-day administration of DHEA on GnRH gene expression in brain of sham-operated and castrated animals of both sexes. In the male rat, orchiectomy induced an increase in the hybridization signal. In sham-operated animals, DHEA decreased GnRH mRNA levels induced by orchiectomy. In orchiectomized rats, DHEA also depressed the amount of mRNA levels and then reversed the increase in mRNA levels induced by orchiectomy. In female animals, as observed in the male, castration produced an increase in the hybridization signal. In both sham-operated and ovariectomized animals, DHEA administration increased mRNA levels. These data clearly indicate that DHEA administration can modify neuronal GnRH gene expression in adult rats of both sexes, the effect being inhibitory in the male and stimulating in the female. This modulation of GnRH neuronal activity, which is probably exerted following the conversion of DHEA into active sex steroids, might be at least partly responsible for modifications of the activity of the hypothalamo-pituitary-gonadal axis induced by DHEA.

Hormonal regulation of sulfated glycoprotein-1 synthesis by nonciliated cells of the efferent ducts of adult rats.

The objective of this study was to define the factors regulating the endogenous production of sulfated glycoprotein-1 (SGP-1) in nonciliated cells of the efferent ducts. To this end we examined five different groups of animals undergoing the following experimental procedures: (1) hypophysectomized animals at 7, 14, and 28 days, (2) 7-day hypophysectomized rats receiving testosterone implants given at various time intervals thereafter, (3) castration at various time intervals up to 7 days, (4) 7-day castrated rats receiving testosterone implants at various time intervals thereafter, and (5) castrated rats given testosterone implants immediately after castration and sacrificed at different time intervals thereafter. Efferent ducts were fixed by perfusion with 4% paraformaldehyde and 0.5% glutaraldehyde in phosphate buffer for quantitative immunocytochemical analysis at the level of the electron microscope. For each experimental condition and their controls, the number of gold particles/micron2 within the endosomal and lysosomal compartments was calculated taking into account the changes in both the volume of the cell and organelles being quantified and expressed as labeling content. The results revealed that hypophysectomy (up to 4 weeks) caused a marked significant decrease in the SGP-1 labeling content of the endosomal and lysosomal compartments. The labeling content of the lysosomal compartment of efferent ducts from rats castrated for up to 1 week did not change significantly. However, there was a significant decrease in the labeling content of endosomes. This decrease is due to SGP-1, which is secreted by Sertoli cells, not being available for uptake in the efferent ducts. These results suggested that testosterone is not required for maintaining the high labeling content of SGP-1 within lysosomes of nonciliated cells, but that a pituitary factor appears to be needed. The administration of testosterone at different intervals to 7-day castrated animals resulted in a significant decrease of lysosomal SGP-1, suggesting that testosterone under these experimental conditions inhibits the production of a pituitary factor that maintains the high labeling content of SGP-1 within lysosomes of the nonciliated cells. Testosterone administered to 7-day hypophysectomized animals over a 24-hr period had no effect on the labeling content of SGP-1 within lysosomes. However, the administration of testosterone to animals immediately following castration showed no differences in the labeling content of SGP-1 within compared to controls.(ABSTRACT TRUNCATED AT 400 WORDS)

Glycosaminoglycans of guinea pig prostate fibromuscular stroma: Influence of estrogen and androgen on levels and location of chondroitin sulfate

The effects of aging and hormone manipulation on the glycosaminoglycan (GAG) content of prostatic stroma in guinea pigs were investigated. Total GAG and individual GAG classes (chondroitin, dermatan, and heparan sulfates, and hyaluronic acid) were measured biochemically in stromal extracts. Chondroitin sulfate was also measured and localized by video image analysis of immunocytochemically-stained tissue sections. The weight and total GAG (uronic acid) content of prostatic stroma increased between the ages of 2 weeks and 2 years by 7-8-fold and 4-5-fold respectively. GAG concentration per unit weight of stroma declined 4-fold during puberty and remained essentially unchanged thereafter. Similar results were obtained for each of the GAG classes. The decreases in GAG concentration were associated with a 3-fold increase in the size of the smooth muscle cells of the prostatic stroma during puberty. Hormonal control of GAG deposition in the prostatic stroma was investigated by steroid replacement in prepubertally-castrated animals. Administration of dihydrotestosterone (DHT) to castrate animals for 6 weeks resulted in significantly reduced concentrations of stromal uronic acid, compared with untreated castrate animals (P < 0.05). The GAG levels post-DHT treatment were similar to those observed after pubertal development in sham-operated control animals. Estradiol treatment had the opposite effect to that of DHT, resulting in a significantly increased concentration of uronic acid compared with castrate animals (P < 0.05). These steroid-induced changes in stromal GAG deposition were mostly contributed to by chondroitin and dermatan sulfates. Combined treatment with DHT and estradiol resulted in stromal uronic acid concentrations similar to those of animals receiving DHT alone, indicating that the effect of DHT on stromal GAG deposition is dominant over the effects of estradiol. Morphometric measurement, using computer-assisted video image analysis of a chondroitin sulfate epitope in prostatic sections stained with a monoclonal antibody (6C3), supported the biochemical data. Stereometric profiles across several sectioned glands demonstrated that chondroitin sulfate was confined to the periacinar basement membranes of the prostatic stroma in all groups except the estradiol-treated castrate animals, where the immunostaining extended from the periacinar basement membrane throughout the fibromuscular stroma. Treatment of castrate animals with estradiol alone also induced a physicochemical change in the chondroitin sulfate molecule, resulting in reduced electrophoretic mobility. In summary, this study identifies changes in the quantity, structure, and localization of chondroitin sulfate in the prostatic stroma of estradiol-treated guinea pigs. Furthermore, estradiol and DHT have opposing effects on the level of chondroitin and dermatan sulfate expression in the prostatic stroma.

Dehydroepiandrosterone-Induced Peroxisome Proliferation in the Rat: Evaluation of Sex Differences

Dehydroepiandrosterone (DHEA) is a newly identified peroxisome proliferator that causes hepatomegaly, peroxisome proliferation, and induction of peroxisome-associated enzymes in rats and mice, and hepatocellular carcinomas in rats. In the present study, we have systematically analyzed sex differences and the effect of castration on DHEA-induced peroxisome proliferation in male and female rats, since no information is available on this subject. DHEA was fed in diet at a concentration of 0.45% for 2 weeks and livers were analyzed for hepatomegaly, peroxisome volume density, peroxisome proliferator associated Mr 80,000 polypeptide (PPA-80), and enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase (PBE) mRNA. Both intact and castrated rats showed similar response to DHEA characterized by increased peroxisome volume density, PBE mRNA, and PPA-80. Significant difference was observed in the liver weights between castrated and intact animals in both the sexes. Castrated rats that received DHEA had 20%-30% more liver weight than DHEA-administered intact rats. These results clearly indicate that peroxisome proliferative effect of DHEA is not influenced by sex hormones and it is equally potent in both males and females.

The time since castration influences the effects of short-term starvation on gonadotrophin secretion in male rats

Short-term starvation suppresses the pituitary-testicular function in rats, evidently through inhibition of gonadotrophin-releasing hormone (GnRH) release. However, when gonadotrophin secretion is strongly enhanced, e.g. after castration, starvation does not suppress gonadotrophins. To test whether the time since castration affects the pituitary response to starvation, adult male rats were totally deprived of food for five days (only water allowed) immediately (acute castration) or two weeks after castration (chronic castration). The pituitary contents of GnRH receptors were decreased by starvation in sham-operated animals, unaffected in acutely castrated rats, but increased in chronically castrated animals, in comparison with appropriate controls (P < 0.01). Castration per se increased steady-state mRNA levels of the common alpha-chain and the LH and FSH beta-chains in all groups studied. The only consistent effect of starvation on these parameters was the 1.7 to 2-fold increase in the pituitary content of LH beta-subunit mRNA in acutely and chronically castrated rats (P < 0.01). Starvation alone suppressed LH secretion, acute castration eliminated this effect, but in chronically castrated rats, the starvation effect was stimulatory. Starvation did not affect FSH secretion in sham-operated and acutely castrated rats, but after chronic castration, the effect was stimulatory. In conclusion, the overall effect of starvation on gonadotrophins shifts gradually after castration from suppression, in sham-operated rats, to stimulation, in chronically castrated animals. Parallel changes in pituitary GnRH receptors suggest similar changes in GnRH secretion. Hence, starvation has both negative and positive effects on the GnRH-gonadotrophin-axis. The negative effect is evidently androgen-dependent and dominates in testes-intact animals. After chronic castration, only the positive, non-androgen dependent, stimulatory effect remains.

Seasonal variations in the ultrastructure and production of androgen-dependent proteins in the seminal vesicles of a Saharian rodent (Psammomys obesus)

The effects of seasonal variations and experimental deprivation and substitution of androgen in the seminal vesicles of the Saharian rodent Psammomys obesus were investigated. Cytological studies showed that, during the breeding season, epithelial cells had large amounts of rough endoplasmic reticulum (RER) and substantial apocrine secretion. During the non-breeding season, RER cisternae were no longer expanded and apocrine secretion was rare. Castration during the breeding season was followed by regression of the RER and the disappearance of apocrine secretion. Treating castrated animals and animals in the non-breeding season with testosterone for 15 days caused reactivation. Eight major proteins with molecular weights of 120, 78, 67, 41, 37, 34, 21 and 14.4 kDa were present in homogenates during the breeding season; six (92, 41, 36, 35, 21 and 14.4 kDa) were found in seminal vesicle secretions. During the non-breeding season, the very large amounts of the 21 kDa protein were greatly reduced; conversely the 45 kDa protein increased. Electrophoretic patterns of homogenates from animals castrated during the breeding season showed eight proteins differentially induced (37, 34, 21 and 18 kDa) or repressed (67, 45, 38 and 35 kDa) by testosterone, of which the 21 kDa protein decreased most dramatically after castration. The effects of castration were reversed by the administration of testosterone. During the non-breeding season, the synthesis of the four induced proteins was stimulated by testosterone treatment; conversely that of the 45 kDa protein was suppressed.

Non-steroidal antiandrogens: Synthesis and biological profile of high-affinity ligands for the androgen receptor

New N-substituted arylthiohydantoin antiandrogens were synthesized. These compounds presented exceptionally high relative binding affinities (RBAs) for the rat androgen receptor (AR): up to 3 times that of testosterone (T) and 100 times the RBAs of non-steroidal antiandrogens such as flutamide, Casodex and Anandron. Furthermore, unlike available markers for AR, they were totally devoid of any binding to the other steroid receptors. RU 59063, the molecule with the highest RBA, was tritiated. When it was compared to [ 3H]T for the assay of rat, mouse, hamster and AR, it gave rise to the same number of binding sites but its K a (6×10 9 M −1) for rat and human AR were, respectively 3 and 8 times higher than that of T. Moreover RU 59063, unlike T, was devoid of any specific binding to human plasma. In vivo, these compounds displayed antiandrogenic activity while being devoid of any agonistic effect. Thus, RU 56187, given orally in castrated male animals, prevented in a dose-dependent manner the effects of 3 mg/kg testosterone propionate (TP) on mouse renal ornithine decarboxylase (acute test) and of 0.5 mg/kg TP on rat prostate weight (chronic test). In these two models, its ED 50 was 0.6 and 1 mg/kg, respectively. In the intact rat, when given alone, it inhibited dose-dependently the effect of endogenous androgens on the seminal vesicles (ED 50 ≈ 1 mg/kg) and prostate (ED 50 ≈ 3 mg/kg) weights. These results suggest that these new compounds may be useful as specific markers for the androgen receptor as well as for the treatment of androgen-dependent diseases or disorders such as prostate cancer, acne, hirsutism and male pattern baldness.

Differential effects of aromatase inhibition on luteinizing hormone secretion in intact and castrated male cynomolgus macaques.

To understand the role of central aromatization in feedback regulation of LH in nonhuman primates, we treated adult male cynomolgus monkeys with the aromatase inhibitor, 1,4,6-androstatriene-3,17-dione (ATD). We measured LH, testosterone (T), and ATD in systemic sera of blood samples drawn on a diurnal schedule (0900 and 2100 h). Each animal was bled for 4 pretreatment days from a femoral catheter after which they were divided into the following treatment groups: castrated (Cx), n = 2; Cx + T, n = 6; Cx + T + ATD, n = 6; Cx + ATD, n = 3; and sham operated + ATD, n = 3. Silastic capsules or packets containing T or ATD, respectively, were placed sc between the scapulae at the time of Cx or sham treatment. In T-treated animals, T (20 micrograms/kg body weight) dissolved in propylene glycol was injected im at 2100 h to mimic the diurnal rise of T observed in nonhuman primates. Animals were bled for 2 weeks after which they were killed, and selected brain areas were analyzed for aromatase activity and cytosolic and nuclear androgen receptors. Animals treated with ATD had significantly reduced levels of aromatase activity in selected regions of the hypothalamus, preoptic area, and the amygdala (P < 0.05). Even though ATD inhibited brain aromatase activity, it did not prevent the negative feedback actions of T on LH secretion after Cx. In addition, ATD by itself inhibited LH secretion after Cx and activated brain androgen receptors. These latter effects of ATD seemed to have been mediated through a metabolite. In sham-operated intact males, ATD produced variable surges of LH that were accompanied by elevations of T in the systemic circulation. These differential effects of ATD in intact vs. castrated animals demonstrate the importance of selecting the proper model system to study LH control mechanisms. In the intact animal, aromatization seems to play a role in regulating LH secretion, but the postcastration rise of LH seems to be regulated differently.

Evidence that neuropeptide Y could represent a neuroendocrine inhibitor of sexual maturation in unfavorable metabolic conditions in the rat

Neuropeptide Y (NPY) is known to be involved in the central regulation of appetite, sexual behavior and reproductive function. Whereas central administration of NPY strongly stimulates feeding, diet restriction produces overexpression of NPY in the arcuate and paraventricular nuclei that might reflect behavioral adaptations to shortage of food. The role of NPY for the regulation of sexual function is still controversial. Whereas NPY is stimulatory during proestrus in the rat, acute administration of NPY is inhibitory in castrated animals and we have shown that chronic administration of NPY inhibits both the gonadotropic and somatotropic axis in adult female rats. In order to further analyse the role of NPY during sexual maturation, a model of delayed sexual maturation imposed by food restriction and return to ad-libitum feeding was used. Young female rats were restricted to 7-8 g food daily starting at 24 days of life (d). This restriction completely prevented sexual maturation. At 50 d, ICV cannulas were placed and at 60 d, Alzet minipumps either delivering NPY (18 micrograms/day) or vehicle into the ICV cannula were implanted dorsally. At 61 d, rats were switched to ad-libitum feeding, a change that produced vaginal opening within 4 days in all vehicle-treated rats. In the rats receiving NPY, significantly increased food intake and weight gain were observed but only one out of the 9 rats studied experienced vaginal opening at 66 d, the other 8 animals remaining sexually immature at 67 d at sacrifice. Sexual immaturity of NPY-treated rats was further confirmed by decreased ovarian weight and reduced number of pituitary GnRH receptors. Plasma IGF-I levels were markedly reduced in NPY-treated rats. Since food restriction has been shown both to increase hypothalamic NPY and to reduce or inhibit sexual function, these data bring evidence for the first time that NPY could be involved in the inhibition of sexual maturation imposed by food restriction, since maintenance of elevated NPY levels in the hypothalamus did prolong this state of sexual immaturity despite restoration of normal food intake.

Evidence that neuropeptide Y could represent a neuroendocrine inhibitor of sexual maturation in unfavorable metabolic conditions in the rat.

Neuropeptide Y (NPY) is known to be involved in the central regulation of appetite, sexual behavior and reproductive function. Whereas central administration of NPY strongly stimulates feeding, diet restriction produces overexpression of NPY in the arcuate and paraventricular nuclei that might reflect behavioral adaptations to shortage of food. The role of NPY for the regulation of sexual function is still controversial. Whereas NPY is stimulatory during proestrus in the rat, acute administration of NPY is inhibitory in castrated animals and we have shown that chronic administration of NPY inhibits both the gonadotropic and somatotropic axis in adult female rats. In order to further analyse the role of NPY during sexual maturation, a model of delayed sexual maturation imposed by food restriction and return to ad-libitum feeding was used. Young female rats were restricted to 7-8 g food daily starting at 24 days of life (d). This restriction completely prevented sexual maturation. At 50 d, ICV cannulas were placed and at 60 d, Alzet minipumps either delivering NPY (18 micrograms/day) or vehicle into the ICV cannula were implanted dorsally. At 61 d, rats were switched to ad-libitum feeding, a change that produced vaginal opening within 4 days in all vehicle-treated rats. In the rats receiving NPY, significantly increased food intake and weight gain were observed but only one out of the 9 rats studied experienced vaginal opening at 66 d, the other 8 animals remaining sexually immature at 67 d at sacrifice. Sexual immaturity of NPY-treated rats was further confirmed by decreased ovarian weight and reduced number of pituitary GnRH receptors. Plasma IGF-I levels were markedly reduced in NPY-treated rats. Since food restriction has been shown both to increase hypothalamic NPY and to reduce or inhibit sexual function, these data bring evidence for the first time that NPY could be involved in the inhibition of sexual maturation imposed by food restriction, since maintenance of elevated NPY levels in the hypothalamus did prolong this state of sexual immaturity despite restoration of normal food intake.

Transcriptional regulation of dog prostate arginine esterase gene by androgens

These studies were designed to define the molecular events involved in the modulation of dog prostate arginine esterase gene expression following short castration intervals and androgen treatment. Arginine esterase enzymatic activity and protein levels decreased about 50% 24 h after castration. Thereafter, a more progressive decrease was observed, resulting in 2-4-fold lower levels in 12-day castrates than in the intact controls. Total prostatic arginine esterase mRNA levels slowly decreased during the first five days after castration but more abruptly thereafter and were about 150-fold lower in 12-day castrated animals. By contrast, in isolated prostatic nuclei, levels of arginine esterase RNA precursors and mature transcripts rapidly fell following orchiectomy, with a 50–70% decrease 24 h after castration. Nuclear run-on experiments confirmed that the latter effects were the result of decreased arginine esterase gene transcription. All these changes could be at least partially reversed by administration of testosterone cypionate. Furthermore, no striking modifications in the proportion of epithelial/stromal cells in the prostatic tissue were observed following orchiectomy. These results show that castration and androgens exert very rapid effects on the gene expression of arginine esterase, and that the regulation occurs at the transcriptional level.

Biphasic effect of exogenous testosterone on follicle-stimulating hormone gene expression and synthesis in the male rat

Effects of 2-week treatments with increasing doses of testosterone (T) on gonadotropin gene expression and secretion were studied in intact and acutely castrated male rats. T was administered in silastic capsules with lengths of 2, 4, 8 or 16 cm, and control animals received empty capsules (eight per treatment). The treatments increased serum T up to 3-fold of control levels. In intact animals, the 2–8 cm capsules suppressed pituitary follicle-stimulating hormone-β (FSHβ) mRNA contents by 40–50% ( p < 0.01), but 16 cm of T returned the levels back to control range. Castration alone increased the FSHβ mRNA level 2.3-fold ( p < 0.01) and, after T treatment, the FSHβ message returned to control levels indistinguishable from intact controls but higher than in intact animals receivimg the same T dose. Pituitary luteinizing hormone-β (LHβ) mRNA displayed a dose-dependent suppression in response to T, to 32–35% of controls ( p < 0.01) with the 8 and 16 cm capsules. Castration increased this message 10-fold, and additional T treatment suppressed the levels to the range of T-treated intact animals. Pituitary common-α mRNA decreased to 30–31% of controls by 2, 4 and 8 cm of T ( p < 0.01), but the highest dose of T increased the common-α contents, in comparison to the other doses, to 54% of controls ( p < 0.01). Castration alone increased the common-α contents 4.4-fold, and there was a dose-dependent suppression of this parameter by T down to the range of T-treated intact rats. The pituitary FSH contents of intact and castrated rats also displayed a biphasic T response: suppression by low doses and recovery by higher doses. Despite the clear stimulation in the gene expression and pituitary content of FSH with the highest T dose, no evidence for increased secretion was found. A monophasic dose-dependent suppression of pituitary LH by T occurred in intact and castrated rats. Serum LH decreased with all T doses in intact and castrated animals ( p < 0.01), and the 8-fold increase after castration was reversed with all T doses ( p < 0.01). The T treatments had no effect on serum inhibin levels, neither were there changes in the levels of inhibin subunit mRNAs by T treatment. The weight of the testis was reduced by 2–8 cm T treatments ( p < 0.01), but 16 cm of T reversed the weight to control level. In conclusion, T treatment has a biphasic effect on the gene expression and synthesis of FSH in intact and castrated male rats. However, FSH secretion is not increased by high doses of T, evidently due to suppressed gonadotropin-releasing hormone (GnRH) secretion. Only negative effects of the different doses of T were observed on LH gene expression, synthesis and secretion. Inhibin gene expression and secretion were not affected by T.