Adrenal gland involvement in the regulation of renal 11beta-hydroxysteroid dehydrogenase 2

Renal 11beta-hydroxysteroid dehydrogenase 2 (HSD2) catalyzes the conversion of active glucocorticoids to inert 11beta-keto compounds, thereby preventing the illicit binding of these hormones to mineralocorticoid receptors (MRs) and, thus, conferring aldosterone specificity. Absence or inhibition of HSD2 activity, originates a hypertensive syndrome with sodium retention and increased potassium elimination. Recent studies from our laboratory reported an increment of HSD2 activity in intact-stressed rats. To evaluate the adrenal involvement in this increase, we analyzed HSD2 activity and protein abundance in Intact, Sham-operated, and adrenalectomized rats under stress situations (gavage with an overload of 200 mM HCl (10 ml) and simulated gavage) or with corticosterone replacement. HSD2 activity was assessed in renal microsomal preparations obtained from different groups of animals. HSD2 protein abundance was measured by Western-blot. Circulating corticosterone was determined by radioimmunoassay. Sham-operated animals showed an increase in HSD2 activity and abundance compared to Intact and adrenalectomized rats suggesting the involvement of stress-related adrenal factors in HSD2 regulation. In the case of acidotic adrenalectomized animals, there was an increase in renal HSD2 activity when, along with the HCl overload, the rats were injected with corticosterone. This increment occurred without an increase in enzyme abundance. These results suggest the importance of circulating levels of glucocorticoids to respond to a metabolic acidosis, through regulation of HSD2 stimulation. The group subjected to a simulated gavage showed an increase in enzyme activity and protein abundance, thus demonstrating the need for both adrenal and extra-factors in the modulation of renal HSD2. The adrenalectomized animals injected with different doses of corticosterone, produced a progressive increase in enzyme activity and abundance, being significant for the dose of 68 microg corticosterone/100 g body weight. The highest dose (308 microg/100 g body weight) did not show any variation in activity and abundance compared to the control group. This biphasic effect of glucocorticoids could be explained taking into account their permissive and suppressive actions, depending on their blood levels. Knowing that stress induces multifactorial responses, it should not be surprising to observe a differential regulation in renal HSD2, confirming that different stressors act through different factors of both, adrenal and extra-adrenal origin.     

Serotonin involvement in the inhibition of luteinizing hormone (LH) release during immobilization in castrated male rats

The involvement of serotonin in mediating the inhibitory effect of immobilization stress on LH secretion in castrated male rats was examined by employing p-chlorophenylalanine (PCPA, 320 mg/kg, ip), an inhibitor of serotonin synthesis, and 5,6-dihydroxytryptamine (5,6-DHT, 50 micrograms, icv), a drug toxic to the indoleaminergic system. Immobilization stress suppressed pulsatile LH release and decreased mean plasma LH levels. Pretreatment with PCPA or 5,6-DHT apparently eliminated the inhibitory effect of immobilization stress on LH release. These results suggest the possible involvement of a serotoninergic mechanism in mediating the suppression of LH release induced by immobilization stress in castrated male rats.     

Galanin regulation of LH release in male rats

The present study examines the role of cerebroventricular administered (IIIrd ventricle) galanin on LHRH and LH release in adult and immature male rats. In both age groups, galanin stimulated LHRH synthesis and release from the hypothalamus, leading to a higher release of pituitary LH which in turn increased plasma LH levels. Galantide, a galanin receptor blocker, on the other hand, drastically reduced hypothalamic LHRH and plasma LH while increasing pituitary LH. In vitro incubation of anterior pituitary cells with galanin followed by LHRH resulted in increased release of pituitary LH but not by galanin alone. Galantide exhibited no such effect either alone or with LHRH. These results indicate that galanin is an important regulator for both hypothalamic LHRH and hypophysial LH and its role is independent of age in the case of male rats.     

Increased fertility in rhesus monkeys by breeding after the preovulatory LH surge.

Fertility in a rhesus monkey breeding colony was significantly increased by caging females with males immediately after detection of the preovulatory luteinizing hormone (LH) surge. LH was measured in daily serum samples by a rapid (24-hr) radioimmunoassay which used iodinated ovine LK as tracer and an antiserum to human LH.     

Effects of ovarian hyperstimulation and isolated preovulatory follicles on LH responses to GnRH in rats

Adult rats were pretreated with a 3-day regimen of human menopausal gonadotrophin (hMG), PMSG, human FSH or hCG and experiments were carried out on the day of pro-oestrus. Treatment with hMG and hFSH induced a significant increase in the number of preovulatory follicles on the day of pro-oestrus and this was correlated with increased circulating concentrations of oestradiol. There was a parallel increase in the self-priming effect of GnRH, as observed from the biphasic LH response to a continuous GnRH challenge. PMSG treatment did not stimulate increased numbers of maturing follicles and was less effective in raising circulating oestrogen concentrations compared with hMG and hFSH. However, pituitary responsiveness was much higher after PMSG treatment and the biphasic response to continuous perfusion with GnRH was absent; LH release was high from the initiation of the stimulus. hCG alone failed to stimulate follicular maturation but enhanced pituitary LH responses. Hemi-pituitary glands perfused in the presence of isolated preovulatory follicles also showed augmented biphasic LH responses to GnRH compared with control hemi-pituitary glands. The apparent dissociation which can occur between follicular maturation, circulating oestrogen concentrations and pituitary responsiveness to GnRH supports the idea of non-steroidal ovarian factors modulating LH release.     

Effect of ethanol in preovulatory periods on LH, FSH, prolactin and ovulation in rats

The effect of ethanol (4 g/kg) as well as the role of serotoninergic neurons on the rate of ovulation and plasma LH, FSH and prolactin secretion have been studied in rats at preovulatory periods (18th hour of diestrus). It has been found that administration of ethanol in preovulatory periods decreased the number of ovules per rat (p less than 0.001), the number of ovulating rats and LH levels (p less than 0.001). These effects were accompanied by an increase in prolactin concentration (0.05 greater than p greater than 0.02), which was followed by a diffuse luteinization in the ovarian tissue. These results showed that ethanol had an effect of central depression in preovulatory periods. These effects could be mediated through the hypothalamic releasing factors. Under previous serotonin depletion with p-chlorophenylalanine (PCPA: 300 mg/kg), ethanol caused similar effects on LH and FSH levels as compared with the control group with PCPA. However, prolactin concentration was not increased. These results showed that serotoninergic neurons could be mediated in changes caused by ethanol on prolactin secretion, but do not affect directly in changes caused on LH and FSH secretion.     

Blockade of the preovulatory release of gonadotropins and prolactin by spinal transections in female rats

The effect of spinal transections on the preovulatory release of gonadotropins and PRL was investigated in female rats. A preovulatory rise in serum LH, FSH and PRL and subsequent ovulation were prevented by complete spinal transections (CST) at high thoracic levels (T3-T7), but not at low thoracic and lumbar levels (T8-L5), performed at 1000-1230 h on proestrus. Norepinephrine (NE) concentrations in the preoptic-anterior hypothalamic area at 1700-1800 h on proestrus were also significantly reduced by CST at high thoracic levels, but not at lumbar levels. Either electrochemical stimulation of the suprachiasmatic part of the preoptic area or NE injection into the third ventricle at 1400-1500 h on proestrus restored ovulation in animals with CST at high thoracic levels. Animals with CST at lumbar levels exhibited relatively regular 4-day cycles, but those with CST at high thoracic levels showed prolonged periods of diestrous (8-20 days) before they resumed cyclicity. In the case of partial transections, bilateral transections of the lateral columns, but not transections of the dorsal or medial columns, of the spinal cord at T4-T5 significantly blocked the preovulatory gonadotropin release and the occurrence of ovulation. Unilateral transections of the lateral columns of the spinal cord or unilateral electrolytic lesions of the ventrolateral part of the medulla oblongata (VLMO) failed to block ovulation. When combinations of them were performed ipsilaterally, ovulation occurred, but when they were performed contralaterally, the incidence of ovulation was significantly decreased.(ABSTRACT TRUNCATED AT 250 WORDS)     

LH secretion around the time of the preovulatory gonadotrophin surge in the ewe

Blood samples were taken once an hour from 17 ewes starting on Day 15 of a natural oestrous cycle and continuing for 4 days or until 36 h after the onset of oestrus. On Days 12, 16, 17 and 18 of the cycle, blood samples were also taken every 5 min for 6 h, between 09:00 and 15:00 h. LH pulse frequency rose and amplitude fell between the luteal and follicular phase of the oestrous cycle ( ). In the period from 48 h before to 40 h past the peak of the preovulatory LH surge, LH pulse frequency did not change. LH pulse amplitude was similar prior to and following the LH surge. During the preovulatory LH surge, LH pulse amplitude rose markedly ( ), with the visible, discrete components of pulses ranging from twice to 20 times those seen prior to or following the surge. The amplitude of LH pulses on the downslope of the LH surge was greater than that on the upslope of the surge (P < 0.05). We conclude that the preovulatory LH surge may consist of an amalgamation of high frequency, high amplitude pulses of LH secretion.     

Adrenal involvement in scrapie-induced obesity

In previous studies we found an increase in body weight during the preclinical phase of disease in certain scrapie strain-mouse strain combinations. The effect was augmented by injection into the hypothalamus. In the present study, we found an increase in food consumption (compared to the normal mouse brain injection group) for both the 139A and ME7 scrapie groups, although only the ME7 group showed an increase in body weight. In a scrapie strain-mouse strain combination that showed an increase in body weight, the adrenal gland was the only organ that showed a significant increase in weight. The titer of scrapie in the adrenals was comparatively low. Adrenalectomy prevented the increase in body weight in two strains of mice injected with the ME7 scrapie strain. The results suggest that scrapie-induced obesity depends on an effect of scrapie on the hypothalamic-pituitary-adrenal axis.     

Evidence for involvement of prostaglandins in central alpha adrenergic activity and LH release in sheep

Circhoral pulsatile release of immunoreactive luteinising hormone (LH) and prostaglandin F2 alpha (PGF2 alpha) occur synchronously into the jugular vein in ovariectomised sheep. Following a 4-hour control period, intra-carotid injections of phentolamine or intramuscular injections of phenoxybenzamine were given to ovariectomised sheep and the pulsatile release of LH and PGF2 alpha was monitored for a further 6 to 8 hours. Phenoxybenzamine caused a fall in LH and PGF2 alpha in jugular venous plasma. Phentolamine also reduced LH significantly but in this case a marked rise in PGF2 alpha as measured by radioimmunoassay (RIA) occurred after very high doses of phentolamine. Interpretation of the latter results was complicated by the fact that phentolamine at high dose levels interfered with the RIA of PGF2 alpha in plasma. Experiments were repeated in ovariectomised sheep with cannulae placed in the lateral ventricles of the brain for sampling cerebrospinal fluid (CSF). In contrast to the previously observed rise in jugular venous PGF2 alpha following high doses of phentolamine, a fall in CSF levels of immunoreactive PGF2 alpha occurred following intracarotid phentolamine or phenoxybenzamine in 3 out of 7 experiments, while no change was observed in the remaining 4 animals. Phentolamine did not reduce LH significantly in animals with intraventricular cannulae. The work provides support for the view that circhoral pulses of immunoreactive PGF2 alpha in sheep are neural in origin and may be related to sympathetic neurotransmission.     

Opiate system involvement in the control of LH secretion in diabetic and normoglycemic male rats

The effect of Naltrexone (Nalt), a specific opiate receptor blocker, on LH secretion was studied at frequent intervals during the first hour following treatment. Nalt was injected i.v. by one bolus (1 mg/rat) to diabetic and normoglycemic rats. Blood samples (0.8 ml) were withdrawn at short intervals after injection, through an indwelling cannula. The diabetic rats responded by secretion of LH, which was lower, but not significantly, than that of normal rats, (peak levels 0.74 +/- 0.17 and 0.97 +/- 0.21 ng/ml respectively). After 45 min., LH levels were in the same range as baseline level in the diabetic group; but were still significantly elevated in the control rats. Thus, it can be concluded that in normal rats, as well as in diabetics, LH secretion as a response to Nalt was episodic in spite of Nalt's long half life time. In order to explain the rapid fall in LH levels after Nalt administration, normal rats were injected with a second bolus of Nalt, 2 hours after the first. The second bolus caused only a blunted response of LH secretion. In another experiment, administration of morphine (1 mg/rat) 2 hours after pretreatment with Nalt did not stimulate the prolactin secretion which normally follows morphine treatment. These results indicate that the rapid decrease of LH levels after Nalt treatment in normal rats is not due to absence of the drug in the system. It is suggested that other neural mechanisms, such as the dopaminergic system, are activated during Nalt influence.