Normal Intact Animals Research Articles

Carleton B. Chapman, MD, MPH

Carleton B. Chapman, who made important contributions in 4 areas of medicine, died in Hanover, New Hampshire, on December 10, 2000. These areas included cardiovascular medicine and research, medical education, philanthropy, and medical history and ethics. His career can be separated temporally into periods when he focused on each of these areas, although he was active in all of them throughout his career. Dr Chapman was born on June 11, 1915, in Sycamore, Alabama (the same small community that produced Tinsley Harrison). He attended public schools in Talladega and graduated from Talladega High School. He was a precociously talented concert organist during his school years, and he seriously considered a career in music. Although he ultimately chose medicine, he maintained his passion for playing the organ throughout his life. He entered Davidson College in 1932 as a liberal arts major, where he became President of the Student Body and a member of Phi Beta Kappa. By the time of his graduation in 1936, he had developed an interest in human physiology, which he pursued at Oxford University after being awarded a Rhodes Scholarship. As a student of St Johns College, Oxford, from 1936 to 1939, he received his BA and MA degrees in Physiology. During that time, he worked with the famous respiratory and exercise physiologist Professor C.G. Douglas. He returned to the United States in 1939 and completed medical school at Harvard, where he received his MD in 1941 and his MPH in 1944. His training in Internal Medicine and Cardiology was received at Boston City Hospital from 1941 to 1944. From 1944 to 1946, he was in the Public Health Service and was stationed first in the Middle East and then in China and Indonesia. In 1946, he returned to Harvard and did a second …

Dipole source localization by mottled sculpin. III. Orientation after site-specific, unilateral denervation of the lateral line system.

To test the hypothesis that spatial excitation patterns along the lateral-line system underlie source localization, we videotaped the orientation behavior of blinded mottled sculpin in response to a small dipole source (50-Hz vibrating sphere) before and after unilateral denervation of the lateral line system on different body regions (head, trunk and head + trunk). Approach pathways were qualitatively similar to those followed by normal intact animals. Abnormal behavior (turning in circles) was not observed. However, the frequency with which fish placed their intact side facing the source increased by 12-89%, depending on the denervation site. The angular accuracy of orientation decreased by 20 degrees to 60 degrees (100% to 370% change) depending on source location and region of lateral line denervated. Deficits tended to be site-specific. For example, unilaterally denervating lateral-line organs on the head resulted in less accurate orienting responses when the source was located on the denervated side of the head, but not on the opposite side of the head or on either side of the trunk. Site-specific deficits and the absence of abnormal approach pathways argue that animals are relying on a point-by-point spatial representation of source location along the sensory surface rather than computations based on bilateral comparisons.

Dopaminergic microtransplants into the substantia nigra of neonatal rats with bilateral 6-OHDA lesions. II. Transplant-induced behavioral recovery

Transplants of fetal ventral mesencephalic (VM) dopamine neurons implanted into the substantia nigra in 6-hydroxy-dopamine (6-OHDA)-lesioned neonatal pups establish axonal connections with the denervated caudate putamen (Nikkhah et al., 1995). In the present study, we have explored the functional capabilities of these animals after they reached adulthood on a battery of spontaneous and drug-induced behavioral tasks. The results demonstrate that unilateral intranigral VM grafts in bilaterally lesioned neonates induce a marked bias in spontaneous- and stress-induced rotation contralateral to the implant not present in the lesion-only controls. Amphetamine and apomorphine induced vigorous contra- and ipsilateral rotation, respectively. Moreover, grafted animals achieved 75% of the performance level in contralateral skilled forelimb use when compared to normal controls, which was significantly above lesion-only animals (50% of normal). Spontaneous nocturnal locomotor activity was elevated 2.2-fold in the grafted animals. Sensorimotor orientation and disengage behavior was spared by the neonatal dopamine lesion and unaffected by the grafts. The level of functional restoration seen in the present study was more extensive than reported previously in neonatally 6-OHDA-lesioned rats where the VM grafts were implanted ectopically into the striatum. However, functional recovery remained incomplete also after intranigral graft placement compared to normal intact animals. The present approach should provide a new promising avenue for the continued exploration of the mechanisms involved in functional recovery and structural repair in the damaged nigrostriatal system.

Enhanced Brain Cell Proliferation Following Early Adrenalectomy in Rats

We have previously demonstrated an increase in adult brain DNA content in rats adrenalectomized on postnatal day 11. The present studies examined cell proliferation in cerebral cortex, cerebellum, hippocampus, and midbrain-diencephalon following adrenalectomy at this age. Compared to sham-operated controls, adrenalectomized animals showed increased [3H]thymidine incorporation into DNA (measured at 1 h following a pulse injection) in all brain regions at 7 and 14 days postsurgery. In some areas, the effect was already present as early as 2 days following adrenalectomy. Chronic replacement with corticosterone prevented this increase in DNA labelling in a dose-dependent manner. When cell proliferation in the cerebral cortex and cerebellum was independently assessed by measuring changes in thymidine kinase activity, enzyme activity was significantly elevated in both areas at 7 and 14 days postsurgery. Finally, histological examination of the cerebellar cortex suggested a delayed disappearance of the external granular layer in several cerebellar lobules of adrenalectomized animals. Overall, these findings indicate that day-11 adrenalectomy leads to a prolonged stimulation of mitotic activity in areas where cell formation at this time is exclusively glial (i.e., cerebral cortex and mid-brain-diencephalon) as well as in areas where postnatal neurogenesis is also occurring (cerebellum and hippocampus). It is hypothesized that this stimulation results from the removal of a tonic inhibitory effect exerted by circulating glucocorticoids in the normal intact animal.

Accessory olfactory bulb transplants correct hypogonadism in mutant mice

Transplantation of normal fetal gonadotropin-releasing hormone (GnRH) neurons from the accessory olfactory bulb (AOB) to the third ventricle of GnRH-deficient adult mutant mice reverses the genetically determined reduction in pituitary hormones and poorly developed gonads. The transplanted heterotopic AOB neurons adapt their morphology and secretory functions to what is observed with preoptic GnRH neurons when transplanted into deficient mice and in the normal intact mature animal. This suggests the presence of median eminence trophic factors affecting the growth, terminal sprouting, and functional behavior of the transplanted neurons.

Characteristics of Separated Epithelial and Stromal Subfractions of Prostate: I. Rat Ventral Prostate

These studies were initiated with the objective of isolating epithelial and stromal cells of human prostatic tissue in undamaged state, in order to study the cellular distribution of steroid receptors in benign prostatic hyperplasia (BPH) relative to normal prostate. Initial experiments showed that when BPH tissue immersed in tissue culture media was progressively fragmented by various cutting procedures, epithelial elements were selectively released as clumps of variable size and individual cells, but that a large percentage of these cells were damaged, as evidenced by their failure to exclude trypan blue (TB). These observations suggested that if tissue framentation were carried out under defined conditions that minimize cell damage, BPH subfractions might be obtained containing a large percentage of undamaged cells. To determine conditions of tissue fragmentation which result in maximal recovery of epithelial cells which exclude TB, rat ventral prostate (RVP) was chosen as a model system. Experiments with RVP revealed that maximal yields of such cells were obtained in “large” epithelial clumps (>30 cells per clump) released under the following conditions: (1) chopping the tissue with razor blades in a large volume (2 ml/100 mg RVP) of a Ca2+-free tissue culture medium (Joklik's-MEM) containing 1% casein, (2) carrying out the entire fractionation procedure in the cold, and (3) maintaining a 1% casein concentration in the medium during chopping, as well as in subsequent washing procedures, to protect cells from proteolytic activity. In large epithelial clumps, cells in the interior of the clump were not stained by TB but the cells at the periphery of the clump were freely permeable to TB. Single epithelial cells and small epithelial clumps (3–10 cells) released by razor blade fragmentation were also permeable to TB. When large epithelial clumps were incubated at 20°C for 90 min, the clumps disaggregated into smaller clumps and morphologically intact single cells, which did not exclude TB. The residual tissue fragments remaining after chopping contained the bulk of stromal cells plus some epithelial elements. The latter could be removed by gentle rubbing of the fragments on a sieve in the presence of medium. The stromal fraction thus obtained consisted of stromal cells, embedded in mesenchymal matrix, which were not stained by TB and appeared normal when examined histologically by light microscopy. The androgen receptor content per unit DNA (AR/DNA) of epithelial clumps and stromal fractions from castrate (1 day) and normal intact rats were compared to control RVP (coarsely minced and washed, but not further dissociated) using [3H]-R-1881 as ligand. In RVP from castrate animals (where AR is unoccupied and cytosolic), the mean AR/DNA ratio in large epithelial clumps was 17% of the control value. However, on a protein basis, AR per milligram cytosolic protein in epithelial clumps was 80% of the unfractioned control. After disaggregation of large epithelial clumps at 20°C, the recovered cells no longer contained detectable levels of AR. The mean AR/DNA ratio in stromal cell fractions from castrate RVP was about half that found in epithelial clump fractions. In RVP from normal intact animals (where AR is occupied with endogenous DHT and predominantly localized in nuclei), AR was measured by a [3H]-R-1881 exchange assay. The mean AR/DNA ratio in epithelial clumps from normal RVP was about 45% of the value found in control tissue; in stromal fractions the mean AR/DNA ratio was about 60% of the found in epithelial clumps. Estradiol receptor (ER) in normal intact rats, measured using [3H]-R-2858 as ligand was found to be unoccupied, cytosolic, and present in low concentration relative to unoccupied, cytosolic AR in castrate RVP. Highest ER/DNA ratios were found in the stromal cellular fraction with successively lower values in unfractionated RVP and epithelial clumps. Arginase activity per unit DNA in epithelial clumps was about 28% of that found in control tissue. The mean arginase/DNA ratio in stromal fractions was about 80% of the value found in the control and consistently higher than in epithelial clumps. Thus in RVP, arginase appears to be a marker for “viability” of stromal as well as epithelial cells, rather than a specific marker for epithelial cells. The present results demonstrate that AR and ER are both present in epithelial and stromal subfractions of RVP. Since AR/DNA ratios were higher in epighelial clumps than in stromal fractions in both normal and castrate RVP, (despite the greater degree of cell damage in epithelial elements relative to stroma, as suggested by arginase content) this finding indicates that AR concentration is much higher in epithelial than in stromal cells. IN contrast, Er appears to be predominantly localized in stromal cells.

Characteristics of separated epithelial and stromal subfractions of prostate: I. Rat ventral prostate.

These studies were initiated with the objective of isolating epithelial and stromal cells of human prostatic tissue in undamaged state, in order to study the cellular distribution of steroid receptors in benign prostatic hyperplasia (BPH) relative to normal prostate. Initial experiments showed that when BPH tissue immersed in tissue culture media was progressively fragmented by various cutting procedures, epithelial elements were selectively released as clumps of variable size and individual cells, but that a large percentage of these cells were damaged, as evidenced by their failure to exclude trypan blue (TB). These observations suggested that if tissue fragmentation were carried out under defined conditions that minimize cell damage, BPH subfractions might be obtained containing a large percentage of undamaged cells. To determine conditions of tissue fragmentation which result in maximal recovery of epithelial cells which exclude TB, rat ventral prostate (RVP) was chosen as a model system. Experiments with RVP revealed that maximal yields of such cells were obtained in "large" epithelial clumps (greater than 30 cells per clump) released under the following conditions: (1) chopping the tissue with razor blades in a large volume (2 ml/100 mg RVP) of a Ca2+-free tissue culture medium ( Joklik 's-MEM) containing 1% casein, (2) carrying out the entire fractionation procedure in the cold, and (3) maintaining a 1% casein concentration in the medium during chopping, as well as in subsequent washing procedures, to protect cells from proteolytic activity. In large epithelial clumps, cells in the interior of the clump were not stained by TB but the cells at the periphery of the clump were freely permeable to TB. Single epithelial cells and small epithelial clumps (3-10 cells) released by razor blade fragmentation were also permeable to TB. When large epithelial clumps were incubated at 20 degrees C for 90 min, the clumps disaggregated into smaller clumps and morphologically intact single cells, which did not exclude TB. The residual tissue fragments remaining after chopping contained the bulk of stromal cells plus some epithelial elements. The latter could be removed by gentle rubbing of the fragments on a sieve in the presence of medium. The stromal fraction thus obtained consisted of stromal cells, embedded in mesenchymal matrix, which were not stained by TB and appeared normal when examined histologically by light microscopy.(ABSTRACT TRUNCATED AT 400 WORDS)

Methoxyindoles and photoreceptor metabolism: activation of rod shedding.

Using an in vitro eye-cup preparation, we have evaluated a potential relationship between methoxyindole metabolism and photoreceptor disk shedding. Melatonin, 6-chloromelatonin, and 5-methoxytryptophol all activate rod disk shedding in culture. The effect is compound specific since serotonin and N-acetylserotonin are without effect, and it is similar to shedding in vivo because it is evoked by light and is quantitatively comparable to a normal intact animal response. The results suggest the involvement of 5-methoxyindoles in the control of rhythmic photoreceptor metabolism.

Alterations in renal tubular water transport induced by parathyroid hormone: evidence for both antidiuretic hormone-mediated and independent effects.

Abstract The renal tubular effects of PTH and ADH are both mediated by cyclic AMP. Furthermore, both of these agents in pharmacological dosage inhibit phosphate reabsorption in the proximal nephron. Although the effect of ADH on tubular water transport is well documented, the actions of PTH on this tubular function have not been studied. We therefore examined the action of PTH on water reabsorption in conscious, chronically TPTX dogs undergoing maximal steady-state water diuresis. The effects of a supraphysiological amount of the hormone (3 to 5 U/kg) were compared to those produced by a dose of PTH (0.3 to 0.5 U/kg) that restores phosphate excretion to a level seen in normal intact animals. In physiological dosage, PTH increased V from 5.6 ± 0.5 to 6.4 ± 0.5 ml/min (p H 2 O as well as C H 2 O factored for GFR × 100 from 4.26 ± 0.39 to 4.88 ± 0.40 ml/min (p H 2 O and CH2OGFR × 100: 4.70 ± 0.33 → 1.76 ± 0.36 ml/min (p AVP levels rose in three of six animals in which it was measured during high-dose PTH infusion, but the levels were falling at a time when urinary osmolality continued to rise. Furthermore, in vitro, PTH and ADH cross-reacted. That is, PTH largely stimulated cortical cyclic AMP, and ADH increased the production of the nucleotide primarily in the medulla. However, in large dosage PTH activated adenylate cyclase in the medulla, and ADH increased the cortical production of cyclic AMP. When PTH was administered in pharmacological dosage to TPTX, hypophysectomized dogs undergoing maximal water diuresis, there was no change in tubular water transport. We conclude the following from these data. (1) PTH, in pharmacological dosage, has an "ADH-like" effect on renal tubular water transport. (2) This action of PTH does not appear to be consistently related to the measurable release of ADH but (3) seems most likely due to an effect of PTH on medullary adenylate cyclase with subsequent alterations in the permeability of the tubular epithelium to water.

Differences in the mechanism of tolerance to dinitrophenylated bovine gamma globulin when induced in normal adult mice or in reconstituted irradiated mice: dependence of the mechanism of tolerance on the structural organization of the lymphoid system.

Tolerance can be induced in adult mice by a single intravenous injection of 0.5 mg dinitrophenylated bovine gamma globulin. The cellular mechanism of the unresponsive state is different depending upon whether the tolerance is induced in normal intact adult mice or in reconstituted, irradiated mice. The tolerant state induced in intact mice is characterized by a high avidity of the residual antibody-forming cells in partially tolerant animals and a prompt reversibility on cell transfer. The overall properties of this unresponsive state are consistent with the hypothesis that it is mediated by the production of small amounts of high affinity antibody in response to the tolerance-inducing injection of antigen. In contrast, the unresponsiveness induced in reconstituted, irradiated mice by the same procedure was characterized by a low avidity of the residual antibody-forming cells in partially tolerant animals and stability on transfer of spleen cells from unresponsive into irradiated recipients. No suppressor cell activity was detected and mixed cell transfer studies were consitent with the view that this unresponsive state represented a B-lymphocyte clonal deletion. The presence or absence of T lymphocytes in the population of cells used for reconstituting the irradiated recipients did not effect the ease of tolernace induction or the cellular mechanism of the tolerant state which was produced. If irradiated mice reconstituted with B and T lymphocytes were rested for 2 wk before tolerance induction then a reversible "high affinity"-type tolerance is obtained such as is typical of normal intact animals. Restorationof a "normal" response to the tolerance-inducing injection of antigen is dependent upon the presence of thymus cells in the population of cells used for reconstitution. It is suggested that the structural integrity of the lymphoid tissue is critical in determining whether B cell will be rendered tolerant after exposure to antigen in vivo.

Effect of a single treatment with the alkylating carcinogens dimethylnitrosamine, diethylnitrosamine and methyl methanesulphonate, on liver regenerating after partial hepatectomy: II. Alkylation of DNA and inhibition of DNA replication

Experiments were carried out to determine whether replication of alkylated DNA could be involved in the initiation of hepatocellular carcinoma which results from a single administration of dimethylnitrosamine (DMN) given after partial hepatectomy. The incidence of tumours is higher when DMN is given during the wave of DNA synthesis induced by the operation than when given in the early prereplicative stage. Therefore the alkylation of DNA in the regenerating liver by DMN given at these times and the effect of DMN on DNA synthesis were investigated. The extent, duration and pattern of alkylation of DNA, including the formation of 0-6-methylguanine, were similar whether DMN was given in the early pre-replicative stage (6 h after the operation) or during the period of DNA synthesis (at 24 h). DMN given a 6 h very greatly reduced the wave of DNA replication which would otherwise have ensued. When given at 24 h, by which time DNA synthesis was already taking place, DMN reduced the rate of incorporation of (-3H)thymidine after 1-2 h delay. However, in neither case was DNA synthesis reduced to the level occurring in normal intact liver. Treatment with diethylnitrosamine (DEN) at 6 h or at 24 h had a similar effect to DMN on the wave of DNA replication induced by partial hepatectomy. Methyl methanesulphonate (MMS given in the early pre-replicative stage delayed the wave of DNA synthesis by about 8 h, but when it did take place the extent of synthesis was as great as in untreated animals. When given during the period of DNA replication, MMS rapidly reduced the rate of synthesis. As in the case of the nitrosamines, synthesis was not reduced to the level occuring in normal intact animals. The difference from the nitrosamines lies in the nature of the alkylated bases formed in DNA. The fact that a single treatment with DMN induces cancer in partially hepatectomised animals but not in intact adult animals is not considered to be due to a gross difference in the nature of the alkylation of DNA. The experiments described support the concept that replication of DNA containing bases which are likely to mispair during replication may be necessary to 'fix' the lesion and thus cause a permanent inheritable change in the genetic material.

Serum glycoprotein synthesis in intact and hepatectomized Walker 256 tumor-bearing rats following glucosamine-1-14C administration.

Incorporation of administered free glucosamine-1-14C into protein-bound hexosamine of the various fractions of the total serum proteins, as obtained by disc electrophoresis, has been studied in normal and in Walker 256 tumor-bearing rats, both in the intact state and following hepatectomy. Normal intact animals demonstrate greater incorporation of labeled glucosamine into a band in the transferrin zone than into the other disc electrophoretic fractions during the 3 h period of observation. The response of tumor-bearing intact animals is characterized by increased incorporation of labeled glucosamine into glycoproteins of the post-albumin zone and decreased incorporation into that in the transferrin zone in comparison with normal animals. Non-tumor-bearing hepatectomized animals fail to incorporate significant labeled glucosamine into any of the glycoprotein fractions of the serum. Tumor-bearing hepatectomized animals, on the other hand, incorporate labeled glucosamine into glycoproteins of the post-albumin zone. These studies support the suggestion that malignant tumor tissue is capable of glycoprotein synthesis and release into the circulation and indicate the gross characteristics of the tumor-produced glycoproteins.

Induction of tyrosine aminotransferase by phentolamine

The characteristics of tyrosine aminotransferase induction by phentolamine in rat liver are described. After an initial lag period of about 60 min, phentolamine produced a marked increase in enzyme activity which reached a maximum in about 3 hr. This effect was eliminated by either actinomycin D or cycloheximide. The relation of the induction by phentolamine to adrenal steroids was studied. Phentolamine was found to increase plasma corticosterone levels in normal intact animals. The induction by phentolamine was almost completely abolished by either adrenalectomy or hypophysectomy. However, if a small dose of hydrocortisone was given to adrenalectomized rats, phentolamine then produced a significant increase in enzyme activity. The administration of amino-glutethimide completely eliminated any increase in plasma corticosterone but did not completely eliminate the enzyme induction produced by phentolamine. It is concluded that at least two factors are operative in the induction of tyrosine aminotransferase by phentolamine—(1) a response to an increased plasma corticosterone concentration, and (2) an additional effect which may be a direct substrate type of induction.

The effect of adrenal demedullation on the blood sugar level of rats subjected to long-term cold stress.

Blood sugar levels and adrenal weights (where possible) were recorded, after a 24-h fast, in normal intact, adrenal-demedullated, and adrenalectomized rats kept at 4 °C for up to 130 days. These were compared with data from control rats kept at 21 °C. Hypoglycemia (relative to the control value) prevailed in both normal intact and, more profoundly, in adrenal-demedullated rats during the first 24 h of chilling but no deaths occurred. Adrenalectomized rats, whose blood sugar level at 21 °C was subnormal, at 4 °C soon showed extreme hypoglycemia and died. More prolonged chilling in normal intact rats resulted in hyperglycemia which lasted until after the 25th day. In contrast, in chilled adrenal-demedullated animals the blood sugar remained at the control level throughout this period. At the 50th day the blood sugar of normal intact animals fell to the control value and remained so thereafter. A similar fall in adrenal-demedullated rats resulted in hypoglycemia, but a rise to control values was recorded from the 75th day. Adrenocortical hypertrophy was generally more extensive in the demedullated animals than in the normal intact animals but was absent in both groups by the 130th day. We conclude that the adrenal medulla, besides helping to provide extra blood glucose during exposure to short-term chilling, is also responsible for the sustained hyperglycemia of rats chilled for prolonged periods and thus assists in their acclimation to long-term cold stress.

Use of tissue culture to restore immunological competence to the neonatally thymectomized mouse.

MILLER1 has reported a lack of development of lymphoid tissue in mice after neonatal thymectomy. These mice had a low lymphocyte count in the peripheral blood, and both spleen and lymph nodes failed to develop germinal centres and only a few plasma cells were found in them. In addition, he found that allogeneic skin which was rejected in 10 or 12 days by normal mice grafted when 5 days old survived and nourished for more than 2 months in animals thymectomized at birth. On the other hand, animals thymectomized at birth which received a syngeneic homograft of thymus at the age of 3 weeks were able to reject allogeneic skin homografts like normal intact animals.

Hypothalamic control of thyrotrophin secretion.

1. By means of the haemagglutination-inhibition technique, it has been possible to measure the plasma and pituitary levels of thyroid-stimulating hormone (TSH) following unilateral and bilateral electrolytic lesions placed in the supraoptic area of the hypothalamus of female rats.2. Unilateral lesions after 8 and 48 hr caused a temporary decrease in the percentage of circulating TSH followed by a return to normal.3. Bilateral lesions caused a fall in plasma TSH to a level 41% below normal at 10 days whereas the pituitary level increased 70%.4. Rats with bilateral symmetrical supraoptic lesions, kept for 3 days at 4 degrees C, had a lower plasma TSH content (23%) and a higher pituitary TSH content (16%) than the sham operated control animals but the levels of pituitary TSH did not show any significant difference (0.100 > P > 0.050).5. Thyroidectomized rats with bilateral lesions kept at 26 degrees C for 3 days had a much lower plasma TSH (39%) and a slightly higher pituitary TSH as compared to the normal intact animals, suggesting that the hypothalamus also influences the synthesis of TSH in the pituitary.6. Thyroidectomized rats with bilateral lesions kept at 4 degrees C for 3 days showed both a plasma and pituitary TSH increase compared to controls at 26 degrees C, suggesting that when a higher demand for thyroid function is present the pituitary gland has some autonomy for both secretion and release of TSH. This autonomy appears to be slight, as there was no statistically significant difference between the pituitary TSH levels of the thyroidectomized animals bearing similar supraoptic lesions and exposed to 4 and 26 degrees C.

The effect of reducing the number of embryos during early stages of gestation on the maintenance of pregnancy in the pig.

The number of embryos has been experimentally reduced during early stages of gestation in the pig by means of partial hysterectomy (du Mesnil du Buisson & Rombauts, 1963). Pregnancy is maintained in animals in which only one embryo remains so long as all the uterus is removed except that portion occupied by the embryo. By contrast, if the embryos are confined to one of the uterine horns, the unilateral pregnancy so established is not maintained unless the non-pregnant horn is removed before the 14th day of the oestrous cycle (du Mesnil du Buisson, 1961). The absence of embryos in one horn leads to regression of corpora lutea and thus complete failure of pregnancy at an early stage. These observations suggest that the presence of embryos in a large part of both uterine horns is necessary to establish and maintain pregnancy. The normal number of ovulations in the pig is between twelve and eighteen. Fertilization rate is generally high (Hancock, 1957) and although some embryonic loss may occur during the first few weeks of gestation, there is usually a large number of embryos distributed within the uterus by the 14th day of the cycle. Ovulation rate from the two ovaries may be uneven, but embryonic migration within the uterus occurs (Corner, 1921; Dziuk, Polge & Rowson, 1964) and establishes an even number of blastocysts in both uterine horns. Thus by the 13th to 18th day of pregnancy, blastocysts have elongated and occupy almost the entire length of the uterus (Perry & Rowlands, 1962). It would be of interest to know how many embryos are necessary in order to establish and maintain pregnancy in normal intact animals. During the course of experiments in which eggs were being collected from pigs soon after mating in order to examine early stages of embryonic develop¬ ment, there was a number of animals in which complete recovery of the eggs was not achieved. Thus a variable number of fertilized or unfertilized eggs was left behind in the Fallopian tubes. The effect on subsequent establishment of pregnancy or return to oestrus was recorded. The experimental animals were twenty-nine cross-bred Large White gilts.

Regulation of circulation by carotid sinus, aortic and cardiopulmonary receptors

Three aspects of circulation regulation by vascular receptors are discussed, with particular attention to involvement of presso- and chemoceptive reflexes in the circulatory homeostasis of the normal intact animal.

Effect of renin, ischemia, and plasma protein loading on the isolated perfused kidney.

Normal renal function has been maintained in an isolated artificial heart-lung, whole-blood perfused rabbit kidney for periods of 2–4 hr. The isolated kidney responds to changes in perfusion pressure, changes in plasma protein concentration, and exposure to a 10-min period of ischemia, in a manner similar to that described for the kidney of the normal intact animal. Elevation of the plasma protein concentration produces a fall in the rate of urine flow, sodium excretion, and creatinine clearance, and a marked proteinuria. The administration of renin produces a marked diuresis, natriuresis, and proteinuria. This effect is also produced by the exposure of the isolated kidney to a 10-min period of ischemia, suggesting that this response may be mediated by a renin mechanism. The responses of the kidney to these two procedures differ only in that ischemia produces an increase in renal blood flow and renin produces a slight reduction in renal blood flow and a more pronounced proteinuria.

Phosphorylase activity in rat uterus after catecholamine administration

The effects of epinephrine, norepinephrine, and isoproterenol on uterine phosphorylase were studied in intact, anesthetized rats. All three agents were found to increase uterine phosphorylase a activity when administered in large doses by intraperitoneal injection. Total phosphorylase activity was unaffected. The time course for the effects of epinephrine on uterine phosphorylase activity and glycogen content was also studied. Peak phosphorylase activation occurred within 5 min after injection, and the effect had disappeared within 1 hr. Increase in phosphorylase a activity was accompanied by a decrease in uterine glycogen levels, which were still depressed at a time when phosphorylase a activity had returned to normal. Epinephrine was shown to stimulate phosphorylase a activity in the uteri of ovariectomized and estrogen-primed rats as well as in normal intact animals. Ovariectomized animals treated with estradiol had higher resting phosphorylase a activity than had normal untreated animals. The relative ability of several adrenergic blocking agents to prevent catecholamineinduced increases in uterine phosphorylase a activity was investigated, It was suggested that the catecholamines produced their effects on the uterus both directly, via β-adrenergic stimulation, and indirectly, via ischemia and resultant tissue anoxia induced by activation of a-adrenergic receptors in the uterine vasculature. The ability of epinephrine to activate uterine phosphorylase when administered by intravenous infusion was also demonstrated.