Progesterone In Ovariectomized Rats Research Articles

Acute ethanol treatment increases level of progesterone in ovariectomized rats

To determine whether an increased level of progesterone in adult female rats after acute ethanol treatment, described previously in our study, is the result of activation of adrenal glands, we analyzed adrenal cortex morphologically and measured serum levels of corticosterone and progesterone in ovariectomized rats. In addition, a possible involvement of the opioid system in an observed phenomenon was tested. Adult female Wistar rats were ovariectomized, and 3 weeks after surgery they were treated intraperitoneally with (a) ethanol (4 g/kg), (b) naltrexone (5 mg/kg), followed by ethanol (4 g/kg) 45 min later, and (c) naltrexone (5 mg/kg), followed by saline 45 min later. Untreated and saline-injected rats were used as controls. The animals were killed 0.5 h after ethanol administration. Morphometric analysis was carried out on paraffin sections of adrenal glands, stained with hematoxylin-eosin, and the following parameters were determined: absolute volume of the zona glomerulosa, the zona fasciculata, and the zona reticularis; numerical density, volume, and the mean diameter of adrenocortical cells and of their nuclei; and mean diameter and length of capillaries. The results showed that acute ethanol treatment significantly increased absolute volume of the zona fasciculata and length of its capillaries but did not alter other stereological parameters. Also, serum levels of corticosterone and progesterone were enhanced. Pretreatment with naltrexone had no effect on ethanol-induced changes. These findings are consistent with our previous hypothesis that an ethanol-induced increase of the progesterone level in adult female rats originates from the adrenal cortex.

Localization of bradykinin B2 receptors in the endometrium and myometrium of rat uterus and the effects of estrogen and progesterone.

In the uterus, bradykinin is a potent inducer of smooth muscle contraction, which is mediated by the bradykinin B2 receptor subtype. However, little is known about the distribution or regulation of this receptor in this tissue. The aim of this study was to localize the B2 receptor in the uterus and determine whether the levels of this receptor were altered during the estrous cycle and modulated by estrogen and/or progesterone in ovariectomized rats. At diestrus, uterine B2 receptors were localized to both the circular and longitudinal smooth muscle layers of the myometrium, the endometrial stroma, the glandular epithelium, and the layer subjacent to the luminal epithelium. B2 receptor levels in both myometrium and endometrium were lowest during early proestrus, when estrogen levels are low, whereas myometrial B2 receptor protein and messenger RNA levels were highest during late proestrous, when estrogen levels peak. Similar findings were observed for the estrogen-supplemented group after ovariectomy, with progesterone appearing to inhibit the estrogen-induced rise in bradykinin B2 receptor density in estrogen/progesterone-treated animals. Using in vitro receptor autoradiography employing the specific B2 receptor antagonist analog, HPP-HOE140, immunostaining with specific antipeptide antibodies generated against the B2 receptor, and in situ hybridization using a specific bradykinin B2 receptor riboprobe, our findings show a discrete distribution of the bradykinin B2 receptor throughout the different layers of the uterus and suggest that bradykinin B2 receptor levels in the rat uterus are regulated by estrogen, and possibly progesterone, in both myometrium and endometrium.

Pharmacokinetics of progesterone in ovariectomized rats after single dose intravenous administration.

The pharmacokinetics of progesterone were characterized in ovariectomized female rats. Progesterone was administered intravenously at a dose of 500 micrograms kg-1. Serum progesterone concentrations were determined by radioimmunoassay. Serum concentrations of progesterone were best described by a two-compartment model with elimination from the central compartment. The distribution and elimination phase half-lives were 0.13 +/- 0.024 (mean +/- SD) and 1.21 +/- 0.21 h, respectively. Elimination of the steroid was rapid with a total clearance of 2.75 +/- 0.42 l h-1 kg-1. Progesterone was widely distributed in the rat with a steady state volume of distribution of 2.36 +/- 0.23 l kg-1, a volume of the central compartment of 0.86 +/- 0.24 l kg-1 and a volume of the peripheral compartment of 1.50 +/- 0.19 l kg-1. The results of this study suggest that the ovariectomized female rat is a suitable animal model for examining the pharmacokinetics of progesterone.

GABAergic Control of Receptivity in the Female Rat

GABAergic neurotransmission has been implicated in the control of the steroid-dependent behavior, lordosis. GABA has dual effects on lordosis: it facilitates lordosis through actions in the medial hypothalamus (mHYP) and it inhibits lordosis through actions in the preoptic area (POA). In the present study, gonadally intact and ovariectomized female rats were behaviorally tested with a sexually active male. Brains were removed from sexually receptive female either 1 or 24 h after behavioral testing. There was a significant difference in endogenous GABA concentration in HYP and POA between receptive, postreceptive and ovariectomized nonreceptive females. Specifically, GABA levels in postreceptive females were higher in the HYP (20%) and lower in the POA (21%) in comparison to receptive females (p less than 0.05). There was also a significant change in binding parameters of 3H-muscimol in the HYP and POA of receptive females as compared to 24 h postreceptive and ovariectomized rats. Attempts to modulate 3H-GABA release from hypothalamic tissue slices by estrogen or progesterone in ovariectomized rats yielded no effect on this parameter.

Ovarian steroids and sexual interaction alter oxytocinergic content and distribution in the basal forebrain

The immunoreactive levels of oxytocin (OXY) were assessed by radioimmunoassay (RIA) and immunohistology after treatments with estradiol or estradiol and progesterone in ovariectomized rats that were mounted or not mounted by males. In micropunches from the medial preoptic area (MPOA) OXY immunoreactive levels increased significantly in estrogen-progesterone-treated receptive animals (mean lordosis quotient (LQ) = 82.9 ± 4.4) that were mounted by males over levels in estrogen-treated unreceptive animals (mean LQ = 2.3 ± 1.3). No other areas demonstrated significant changes in OXY levels across these treatments, although the paraventricular nucleus also had elevated OXY levels in receptive mounted females. In other animals, immunocytochemistry revealed that the number of oxytocinergic perikarya in the MPOA decreased in receptive animals (LQ= 86.7 ± 4.9) that were mounted. The number of oxytocinergic perikarya per 50 μm vibratome section in the lateral subcommissural nucleus was lower in all estrogen-treated groups than in oil vehicle-treated controls. We suggest that the combination of increasing immunoreactive levels of OXY in the MPOA with decreasing numbers of oxytocinergic perikarya indicates that preoptic OXY is moved out of cell bodies, in receptive rats that are mounted by males, to a state that is more accessible to the RIA.

Suppression of lordosis behavior by the putative 5-HT receptor agonist 8-OH-DPAT in the rat.

The administration of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), inhibited the lordosis induced by estradiol benzoate or estradiol benzoate plus progesterone in ovariectomized rats. There was no facilitation of lordosis by 8-OH-DPAT in animals pretreated with a threshold dose of estradiol benzoate. The results are consistent with the view that 8-OH-DPAT is an agonist at 5-HT receptors and provide further support for an inhibition role of central 5-HT in the mediation of lordosis behavior.

Persistence of prolactin (PRL) surges induced by progesterone in ovariectomized rats.

The continuity of PRL surges induced by progesterone was examined. Cycling rats were ovariectomized and simultaneously implanted with Silastic tubes containing progesterone. Administration of progesterone was continued by renewing these tubes every 7 days. Five days after the onset of progesterone treatment, they exhibited high plasma PRL concentration at 3:00 h, which revealed the appearance of nocturnal PRL surge. This was confirmed by the observation at 2 h intervals on Days 6 and 14. On both days, diurnal and nocturnal PRL surges were detected. Contrarily, there was no significant PRL release on Day 21. So, PRL surges might terminate between 10 and 15 days after their onset. Because there was apparent nocturnal surge on Day 21 in rats cervically stimulated one day before, disappearance of PRL surges was not the result of attenuation in responsiveness of pituitary gland to hypothalamic control.These data suggest the existence of a specific central mechanism responsible for the termination of PRL surges even under high progesterone milieu.

Evidence that prolactin does not affect the induction of sexual behaviour by oestradiol and progesterone in ovariectomized rats.

Injection of 2.5 mg of the dopamine receptor antagonist domperidone raised serum prolactin concentrations within 3 h and high prolactin levels were maintained for 12 h in ovariectomized rats pretreated with 2 micrograms oestradiol benzoate (OB). This dose of domperidone stimulated the display of sexual behaviour in ovariectomized OB-treated rats within 3 h of administration. The behavioural effect of domperidone, but not its effect on serum prolactin concentrations, was blocked by adrenalectomy. Daily treatment with domperidone had no inhibitory effect on the subsequent induction of sexual behaviour by OB and progesterone in ovariectomized rats. A slight facilitation of the behaviour was noticed in OB-treated rats given daily domperidone injections, but this effect was cancelled by adrenalectomy. The results suggest that an acute increase in serum prolactin levels has no effect on the induction of sexual behaviour by OB in itself, but can stimulate the secretion of an adrenal product, perhaps progesterone, which facilitates the behaviour. Similarly, constant high levels of prolactin by themselves have no effect on the subsequent induction of sexual behaviour by OB and progesterone.

Role of serotonin in estrogen-progesterone induced luteinizing hormone release in ovariectomized rats

Pharmacological agents were used to manipulate the surge of luteinizing hormone (LH) induced by progesterone in ovariectomized rats primed with estradiol benzoate. The LH surge was abolished with p-chlorophenylalanine (PCPA), an inhibitor of tryptophan hydroxylase, and restored by 5-hydroxytryptophan, a serotonin precursor. Serotonin receptor agonists, quipazine and N-N-dimethyl-5-methoxytryptamine, were also capable of inducing an LH surge in rats pretreated with PCPA. The serotonin reuptake blocker chlorimipramine was ineffective in stimulating LH release in PCPA blocked animals. Another reuptake blocker, zimelidine was only partially effective in this regard. These two reuptake blockers, as well as amitriptyline, when injected to non-PCPA treated rats led to the reduction or inhibition of the expected LH surge. Four serotonin receptor antagonists, cyproheptadine, methysergide, cinanserin and SQ-10,631, were each able to reduce or abolish the progesterone induced surge of LH. These results suggest that some of the reuptake blockers of serotonin are also capable of inhibiting receptor binding for this neurotransmitter and strongly indicate that serotonin has a stimulatory role in the steroid induced release of LH in castrated rats.

Colchicine delays the estrogen-induced copulatory response in the ovariectomized female rat

A study was made of the effect of colchicine on the lordotic response to estradiol benzoate (EB) plus progesterone in ovariectomized rats. Colchicine (0.5 + 0.25 mg/kg s.c.) given in connection with the EB treatment inhibited the response elicited by progesterone 24 or 48 h after administration of EB. In contrast, significantly more colchicine-treated animals responded when progesterone was given at 118 h. This increase in lordotic response occurred at a time when normally the response had declined. The response was not enhanced by the protein synthesis inhibitors anisomycin (50 mg/kg s.c.) or cycloheximide (1 mg/kg s.c.). The results suggest that an impairment of axonal transport by colchicine may lead to storage of lordosis-promoting products, which are released when the colchicine effect has worn off.

Serum levels of oestradiol-17 beta and progesterone in relation to sexual receptivity in intact and ovariectomized rats.

Serum levels of oestradiol-17 beta fluctuated markedly during the oestrous cycle or rats. The onset of sexual receptivity occurred in close correlation with increasing serum levels of progesterone. The serum levels of oestradiol and progesterone in ovariectomized rats implanted with constant-release implants filled with oestradiol or progesterone were related to the amount of hormone in the implants. Constant low serum levels of oestradiol stimulated sexual behaviour in ovariectomized rats, but progesterone stimulation was required for maximum behavioural responses. Peak levels of progesterone in the serum during the oestrous cycle were much higher than those needed for induction of the behaviour in ovariectomized, oestradiol-treated rats. Progesterone, administered in physiological doses, inhibited the induction of sexual receptivity caused by oestradiol and progesterone and the inhibition depended on the strength of the stimulation with oestradiol.

EFFECTS OF ACTIVE AND PASSIVE IMMUNIZATION WITH LH-RH ON GONADOTROPHIN SECRETION AND REPRODUCTIVE FUNCTION IN FEMALE RATS

In order to get information about the physiological role played by LH-RH in the regulation of tonic and phasic secretion of gonadotrophins, and about the existence of FSH-RH distinct from LH-RH, we attempted to neutralize endogenous LH-RH by passive and active immunization with LH-RH in female rats. Anti-LH-RH serum prevented pre-ovulatory gonadotrophin surges at proestrus and ovulation, and it suppressed gonadotrophin increase induced by oestradiol benzoate or progesterone in ovariectomized rats. Elevated serum gonadotrophin concentrations in long-term ovariectomized rats were lowered by anti-LH-RH serum injection. The decrease in FSH levels was less than that in LH levels. Serum FSH rose without significant changes in serum LH level for 6 h after ovariectomy on pro-oestrus or dioestrus. The post-ovariectomy rise of FSH was not suppressed by the anti-LH-RH serum which was enought to inhibit serum LH to undetectable levels. Active immunization with LH-RH resulted in decreasing LH levels but failed to alter FSH levels in both serum and pituitary. Seven out of 10 rats immunized with LH-RH became constantly di-oestrous. The weights of anterior pituitary, ovary and uterus of the LH-RH immunized rats were significantly smaller than those of BSA immunized controls. Ovaries of LH-RH immunized rats contained few fresh corpora lutea. These results indicate that LH-RH plays a significant role in the control of both plastic and tonic secretion of LH and FSH. The existence of FSH-RH distinct from LH-RH or mechanism which specially controls the basal FSH secretion is indicated.

The influence of progesterone on adrenocortical function in the rat.

SummaryProgesterone treatment in vivo caused decreased corticosterone and corticosteroid production by homogenates from intact and ovariectomized female rats. Uterine weight, adrenal weight, and plasma corticosterone levels were also reduced by progesterone treatment of intact females. The effect of progesterone in ovariectomized rats indicates that the action of this hormone on in vitro adrenal function may be independent of any modulation of estrogen secretion. Progesterone, in contrast to estradiol and testosterone, has no significant effect on adrenal 5α-reductase activity.

Neural uptake of [1, 2- 3H]progesterone in ovariectomized rats, guinea pigs and hamsters: Correlation with species differences in behavioral responsiveness

The time-course of neural uptake, metabolism, and release of [1, 2- 3H]progesterone was studied in ovariectomized, estrogen-primed rats, guinea pigs, and hamsters in an attempt to correlate species differences in these measures with previously noted differences in behavioral responses to the hormone. The principal findings were: (1) Rat and guinea pig brain took up progesterone in the same pattern; highest uptake was found in the midbrain followed by the hypothalamus, cerebral cortex, and hippocampus. Midbrain uptake was highest in hamster brain, but no consistent uptake pattern was found in the other brain tissues. (2) Guinea pig brain seemed to have a higher affinity for progesterone (indicated by tissue/plasma concentration ratios) than hamster brain, which took up more hormone than rat brain. This pattern was especially striking in midbrain and hypothalamus, where intracerebral progesterone implants have been reported to affect sexual receptivity. (3) Guinea pig and hamster brain retained injected progesterone for a longer time than rat brain. (4) Rat and hamster brain metabolized progesterone more extensively than guinea pig brain. (5) It is suggested that the species differences in neural affinity for progesterone might be responsible for the differential sensitivity to the facilitatory actions of progesterone on estrous behavior. In addition, the prolonged retention of progesterone by guinea pig and hamster brain could be the basis for the post-estrous refractoriness to exogenous hormones found in these species.

Individual differences in sexual responsiveness to estrogen and progesterone in ovariectomized rats

Individual differences among 83 ovariectomized rats in behavioral responsiveness to estrogen were measured by scoring the quality of sexual receptivity induced by injections of estradiol benzoate (EB) and progesterone (P). The P dose remained constant but the quantity of EB administered was systematically reduced over successive weeks until lordosis behavior could no longer be elicited. This EB dose was considered threshold. This sequence of weekly hormone injections and receptivity tests was repeated to assess the reliability of our procedures. Animals had thresholds of either 2.0, 1.0 or 0.5 μg/kg EB on both tests; the correlation between threshold values on the two tests was high (r=0.66; p<0.001). Sixty-two females were used to determine the facilitating effects of various quantities of P following EB treatment. Subgroups were tested after the E alone and again after one of 6 P doses. Zero, 20, 50 and 100 μg P failed to elevate receptivity scores significantly; both 250 and 500 μg P had significant facilitating effects. The results demonstrated that individual differences in EB sensitivity can be measured reliably, and a further analysis also suggests similar individual differences in P responsiveness. Our threshold determination procedures provide a useful technique for measuring the effects of various experimental manipulations on the hormone sensitivity of brain mechanisms which regulate estrous behavior.

Effects of the interruption of amygdaloid and hippocampal afferents to the medial hypothalmus on gonadotrophin release.

SUMMARY The effects of interruption of amygdaloid and hippocampal afferents to the hypothalamus on ovulation and on the release of luteinizing hormone (LH) were studied in rats. Animals acutely deprived on the morning of pro-oestrus of amygdaloid influences either by transection of the stria terminalis (ST) or lesions of the amygdala, failed to show the expected ovulation. Control lesions had no effect. In contrast, rats with long-term transection of either the ST, the cortico-hypothalamic tract (CHT), or both, had regular oestrus cycles and ovulated normally. Studies of ovulation which was induced after the administration of ovarian steroids revealed a differential response to oestrogen and progesterone. In animals with long-term transection of the ST the ovulatory response to oestrogen was similar to that induced in non-lesioned rats but fewer ovulations were induced by progesterone administration. The decreased ovulatory response after progesterone treatment was attributed to activation of inhibitory influences originating in the hippocampus, since administration of picrotoxin or section of the fornix re-established a normal response. Long-term interruption of the limbic efferents did not alter the increased levels of plasma LH found after ovariectomy. However, the release of LH induced by progesterone in ovariectomized rats primed with gonadal steroids was decreased after transection of the ST and increased after interruption of the CHT. These results are consistent with the concept that the amygdala and the hippocampus exert a modulating influence on gonadotrophin release; the influence of the amygdala being facilitatory and that of the hippocampus inhibitory.