Temporal changes in prolactin and corticosterone response during chronic treatment with d-fenfluramine

In order to elucidate the mechanism of development of tolerance to the anorectic effect during chronic treatment with d-fenfluramine (d-F), we examined the temporal changes induced by d-F in food intake and prolactin (PRL) and corticosterone secretion. Male Sprague-Dawley rats were treated for 14 days with d-F (2.5 mg/kg i.p.) or saline twice daily and were given free access to food and water. Groups of 8 rats were sacrificed 30 min after d-F or saline injection at days 1, 4 and 14 for measurements of serum PRL and corticosterone. Food intake and weight gain were reduced significantly by d-F during the first 2-3 days of treatment but not thereafter. Compared with saline, d-F initially increased PRL (57 +/- 9 vs. 7 +/- 0.7 ng/ml) and corticosterone (42 +/- 2 vs. 14 +/- 3 micrograms/dl) serum concentrations. At 4 days, PRL was still significantly increased (43 +/- 5 vs. 10 +/- 4 ng/ml) but corticosterone returned to basal levels. At 14 days, PRL and corticosterone concentrations in the d-F group were not different from corresponding values in the saline group. To verify whether the loss of corticosterone and PRL responses to d-F was not due to a depletion of hormone stores, direct stimulation of corticosterone with corticotrophin and of PRL with metoclopramide were made at days 4 and 14, respectively. Corticotrophin (0.25 mg/kg i.p.) increased corticosterone concentrations similarly in d-F-treated (45 +/- 8 micrograms/dl) and in saline-treated rats (51 +/- 7 micrograms/dl).(ABSTRACT TRUNCATED AT 250 WORDS)     

Interaction of arginine vasopressin and corticotropin releasing factor demonstrated with an improved bioassay

We developed an improved in vivo bioassay for corticotropin releasing factor (CRF) by modifying the injection schedule in the standard chlorpromazine-morphine-pentobarbital assay procedure. A combined injection of chlorpromazine and morphine followed 75 min later by injection of pentobarbital produced low basal levels of corticosterone and rendered the animals highly sensitive to synthetic CRF but insensitive to the stress of ether or histamine. The lowest dose of CRF that significantly elevated plasma corticosterone levels was 0.01 micrograms/kg. Using this assay, we studied CRF-arginine vasopressin (AVP) interactions at doses that were expected to raise systemic peptide concentrations to levels measured in hypophysial portal blood. The threshold for a significant corticosterone response was found to be at least 250-fold lower for CRF-41 than for AVP. The order in which CRF and AVP are injected was also found to be important, potentiation being greater if CRF was given first. In addition, rats deprived of water for 24 hr were more sensitive to CRF than normally hydrated animals.     

New non-steroidal aromatase inhibitors: focus on R76713

R76713 is a novel triazole derivative which selectively blocks the cytochrome P450-dependent aromatase. In human placental microsomes, in FSH-stimulated rat and human granulosa cells and in human adipose stromal cells, 50% inhibition of estradiol biosynthesis was obtained at drug concentrations of 2-10 nM. In PMSG-injected female rats, R76713 lowered plasma estradiol levels by 50 and 90% 2 h after single oral doses of 0.005 and 0.05 mg/kg respectively. After 1 mg/kg, estradiol levels were suppressed by 90% for 16 h. In male cynomolgus monkeys, R76713 dose-dependently (0.03-10 micrograms/kg) inhibited peripheral aromatization with an ED50 of 0.13 microgram/kg without altering metabolic clearance rates and conversion ratios. In vitro R76713 had no effect on other P450-dependent steroidogenic enzymes up to 1000 nM at least. In rats, LHRH-, ACTH- and sodium-deprived diet stimulated plasma testosterone, corticosterone and aldosterone levels were not modified 2 h after single oral administrations of R76713 (up to 20 mg/kg). Furthermore, R76713 did not show any in vitro or in vivo estrogenic or antiestrogenic property. R76713 also induced regression of DMBA-induced mammary tumors after daily oral administration of 1 mg/kg b.i.d. In male volunteers (n = 4), a single oral dose of 5 and 10 mg lowered median plasma estradiol levels from 70 pM to the detection limit of the assay (40 pM) 4, 8 and 24 h after intake whereas no changes were detected after placebo administration. In premenopausal women (n = 15), receiving a single oral dose of 20 mg, median plasma estradiol levels decreased from 389 pM (before) to 168, 133 and 147 pM, 4, 8 and 24 h after intake whereas they remained above 420 pM after placebo (n = 7).     

Chronic corticosterone treatment impairs Leydig cell 11beta-hydroxysteroid dehydrogenase activity and LH-stimulated testosterone production.

The effects of excess corticosterone on luteinizing hormone (LH)-stimulated Leydig cell testosterone production and activity of 11beta-HSD was studied. Adult male rats (200-250 g body weight) were treated with corticosterone-21-acetate (2 mg/100 g body weight, i.m., twice daily) for 15 days. Another set of rats was treated with corticosterone (dose as above) plus LH (ovine LH 100 microg/kg body weight, s.c., daily) for 15 days. Corticosterone administration significantly increased serum and testicular interstitial fluid (TIF) corticosterone but decreased testosterone levels. Administration of LH with corticosterone partially prevented the decrease in serum and TIF testosterone. The oxidative activity of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) was significantly decreased in Leydig cells of rats treated with corticosterone alone and in combination with LH. The direct effect of corticosterone on Leydig cell steroidogenic potency was also studied in vitro. Addition of corticosterone to Leydig cell culture showed a dose dependent effect on LH-stimulated testosterone production. Corticosterone at 50 and 100 ng/ml did not alter LH-stimulated testosterone production, but at high doses (200-400 ng/ml), decreased basal and LH-stimulated testosterone production. Basal and LH-stimulated cAMP production was not altered by corticosterone in vitro. It is concluded from the present study that elevated levels of corticosterone decreased the oxidative activity of 11beta-HSD and thus resulting in impaired Leydig cell steroidogenesis and the inhibitory effects of corticosterone on testosterone production appear to be mediated through inhibition of LH signal transduction at post-cAMP level.     

Concomitant Increases in the Levels of Choline and Free Fatty Acids in Rat Brain: Evidence Supporting the Seizure-Induced Hydrolysis of Phosphatidylcholine

The main objective of this study was to determine whether the excitotoxic cholinesterase inhibitor soman increases the catabolism of phospholipids in rat brain. Injections of soman (70 micrograms/kg, s.c.), at a dose that produced toxic effects, increased the levels of both free fatty acids (175-250% of control) and free choline (250% of control) in rat cerebrum 1 h after administration. All fatty acids contained in brain phosphatidylcholine were elevated significantly including palmitic (16:0), stearic (18:0), oleic (18:1), arachidonic (20:4), and docosahexaenoic (22:6) acids. The changes observed were consistent with those reported to occur following ischemia and the administration of other convulsants. Pretreatment of rats with the anticonvulsant diazepam (4 mg/kg, i.p.) prevented both the signs of soman toxicity and the soman-induced increase of choline and free fatty acids. Diazepam alone did not affect the levels of choline or free fatty acids, cholinesterase activity, or soman-induced cholinesterase inhibition, suggesting that soman toxicity involves a convulsant-mediated increase in phosphatidylcholine catabolism. In addition, administration of the convulsant bicuculline, at a dose that produces seizures and increases the levels of free fatty acids in brain, significantly increased the levels of choline. Results suggest that excitotoxic events enhance the hydrolysis of phosphatidylcholine in brain as evidenced by a concomitant increase in the levels of choline and free fatty acids.     

Evidence that Alterations in γ-Aminobutyric Acid and Acetylcholine in Rat Striata and Cerebella Are Not Related to Soman-Induced Convulsions

Many reports have suggested that gamma-aminobutyric acid (GABA) may play a role in organophosphate-induced convulsions. The balance between GABA and acetylcholine (ACh) in the brain also has been suggested by some investigators to be related to brain excitability. We examined these questions by studying the levels of GABA and ACh and the ratios of GABA to ACh in rat striata and cerebella (two major motor control areas in the CNS) after the administration of soman, an organophosphate acetylcholinesterase inhibitor also known as nerve gas. Male Sprague-Dawley rats weighing 250-300 g were injected subcutaneously with three different doses of soman: a subconvulsive dose of 40 micrograms/kg (approximately 30% of the ED50 for convulsions in rats), a convulsive dose of 120 micrograms/kg (approximately one ED50 for convulsions), and a higher convulsive dose of 150 micrograms/kg (approximately 120% of the ED50 for convulsions). The incidence and severity of convulsions were monitored in individual rats until they were sacrificed by focused microwave irradiation of the head at the following time points after soman administration: 4 min, a time prior to the onset of convulsions; 10 min, the time of onset of convulsions; 1 h, the time of peak convulsive activity; and 6 h, a time at which rats were recovering from convulsions. Results showed that in rat striata and cerebella, neither changes in levels of GABA and ACh nor changes in ratios of GABA to ACh were related to soman-induced convulsions, i.e., none of the changes in either levels or ratios of these two neurotransmitters were related to the initiation of, maintenance of, or recovery from soman-induced convulsions.     

Effects of subchronic pyridostigmine pretreatment on the toxicity of soman

The effect of subchronic pyridostigmine pretreatment on the toxicity of soman, in the absence of supporting therapy (atropine, oxime, and (or) anticonvulsant), as well as its effect on muscarinic cholinoceptor binding characteristics was assessed in the rat. Pretreatment with pyridostigmine by means of an implanted Alzet osmotic minipump for a 5-day total exposure dose of 12 mg/kg inhibited whole blood acetylcholinesterase activity by 73%. This pyridostigmine pretreatment lowered the soman LD50 from 104 micrograms/kg in control animals to 82 micrograms/kg. In addition, the time to onset of soman-induced convulsions in pyridostigmine pretreated animals was significantly (p less than 0.001) reduced. Pyridostigmine pretreatment produced no significant effect on muscarinic cholinoceptor binding in brain or ileum. Lower doses of pyridostigmine pretreatment inhibited acetylcholinesterase activity (65 and 25%); however, LD50 and time to onset of convulsions following soman (140 micrograms/kg) were not significantly different from controls.     

Inhibition of pituitary-gonadal function in male rats by a potent GnRH antagonist

The inhibitory effects of the potent GnRH antagonist, [Ac-D-pCl-Phe1,2,D-Trp3,D-Arg6,DAla10]GnRH (GnRHant) upon pituitary-gonadal function were investigated in normal and castrated male rats. The antagonist was given a single subcutaneous (s.c.) injections of 1-500 micrograms to 40-60 day old rats which were killed from 1 to 7 days later for assay of pituitary GnRH receptors, gonadal receptors for LH, FSH, and PRL, and plasma gonadotropins, PRL, and testosterone (T). In intact rats treated with low doses of the antagonist (1, 5 or 10 micrograms), available pituitary GnRH receptors were reduced to 40, 30 and 15% of the control values, respectively, with no change in serum gonadotropin, PRL, and T levels. Higher antagonist doses (50, 100 or 500 micrograms) caused more marked decreases in free GnRH receptors, to 8, 4 and 1% of the control values, which were accompanied by dose-related reductions in serum LH and T concentrations. After the highest dose of GnRHant (500 micrograms), serum LH and T levels were completely suppressed at 24 h, and serum levels of the GnRH antagonist were detectable for up to 3 days by radioimmunoassay. The 500 micrograms dose of GnRHant also reduced testicular LH and PRL receptors by 30 and 50% respectively, at 24 h; by 72 h, PRL receptors and LH receptors were still slightly below control values. In castrate rats, treatment with GnRHant reduced pituitary GnRH receptors by 90% and suppressed serum LH and FSH to hypophysectomized levels. Such responses in castrate animals were observed following injection of relatively low doses of GnRHant (100 micrograms), after which the antagonist was detectable in serum for up to 24 h. These data suggest that extensive or complete occupancy of the pituitary receptor population by a GnRH antagonist is necessary to reduce plasma gonadotropin and testosterone levels in intact rats. In castrate animals, partial occupancy of the available GnRH receptor sites appears to be sufficient to inhibit the elevated rate of gonadotropin secretion.     

Plasma concentrations of pituitary hormones in 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated male rats

Experiments were conducted to test the hypothesis that acute TCDD toxicity is associated with pituitary hypofunction. Sexually mature male Sprague-Dawley rats were given graded doses of TCDD (0-100 micrograms/kg) and evaluated 7 days later. Despite pronounced hypophagia and body weight loss, plasma concentrations of growth hormone (GH), follicle-stimulating hormone (FSH), and luteinizing hormone (LH) were not significantly affected by any dose of TCDD. Only prolactin (PRL) concentrations were reduced, while, as previously reported, thyroid-stimulating hormone concentrations were elevated. Also, plasma LH, PRL, and adrenocorticotropic hormone (ACTH) concentrations were not significantly affected 1, 2, 3, 4, 5, or 7 days after a single dose of TCDD (50 micrograms/kg). We conclude that (1) pituitary hypofunction is not a major cause of the initial stages of acute TCDD toxicity, (2) growth retardation in TCDD-treated rats is not the result of a deficiency of GH, (3) alterations in plasma corticosterone concentrations are due to altered responsiveness of the adrenal to ACTH stimulation rather than to changes in plasma ACTH concentrations, and (4) that impaired spermatogenesis is not associated with a decrease in plasma FSH concentrations. In addition, the lack of a consistent effect on plasma PRL concentrations suggests that alterations in plasma PRL concentrations do not play a critical role in the toxicity of TCDD. Finally, because TCDD treatment causes a serious androgenic deficiency without increasing the rates at which androgens are catabolized or excreted, the fact that plasma LH concentrations were unaffected indicates that TCDD treatment must reduce the responsiveness of the testis to LH stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Response of exocrine pancreas to corticosterone and aldosterone after adrenalectomy

The long-term effect of adrenalectomy (Adx) on the exocrine pancreas was examined in female adult rats. Pancreatic amylase concentration decrease to 50% of the control level starting 10 days after Adx, whereas the levels of trypsinogen and lipase remained unchanged. Replacement studies beginning 24 h after surgery with corticosterone (B, 1 mg/100 g body wt) or aldosterone (ALDO, 8 micrograms/100 g body wt) alone did not prevent the decline in amylase after Adx. However, when both hormones were administered together, pancreatic amylase concentration was maintained at a level similar to that of the control group. Serum corticosterone levels in the rats receiving B alone or B + ALDO were not different, and were comparable to levels found in normal rats. Both ALDO and B, given for 5 days starting 10 days after Adx, were required to restore amylase concentrations toward control values. When spironolactone (SPIRO, 3 mg/100 g body wt), a specific mineralocorticoid receptor blocker was administered bid together with ALDO + B, it blocked the increase in pancreatic amylase seen in ALDO + B treated rats but did not affect the serum corticosterone levels. These results suggest that mineralocorticoids are also involved in modulating the level of amylase in the rat exocrine pancreas.     

Evidence for suppression of serum LH without elevation in serum estradiol or prolactin with a brain-enhanced redox delivery system for estradiol

We developed a redox system for brain-enhanced delivery of estradiol based on an interconvertible dihydropyridine in equilibrium pyridinium salt carrier. Estradiol (E2), when combined with the lipoidal carrier, readily crosses the blood-brain barrier. The carrier, when oxidized, reduces the rate of exit of the estradiol-carrier complex from the brain. Subsequent hydrolysis of the carrier provides sustained production of estradiol in the brain. The aim of the study was to evaluate the effects of single vs. multiple injections of the estradiol-chemical delivery system (E2-CDS) on both central and peripheral estrogen-responsive tissues. Ovariectomized Sprague-Dawley rats received an intravenous injection of E2-CDS at 10, 33, 100 or 333 micrograms/kg BW or the drug vehicle, dimethyl sulfoxide (DMSO; 0.5 ml/kg) every 2 days for 7 injections (2 weeks) or a single injection only at 2 days before sacrifice. With a single injection, E2-CDS did not affect serum luteinizing hormone (LH) levels at the 10 micrograms/kg dose but caused a dose-dependent reduction in serum LH of 39-52% at the dose range of 33 to 333 micrograms/kg. By contrast, multiple injections of E2-CDS caused a 32 to 76% reduction in serum LH levels at doses ranging from 10 micrograms/kg to 333 micrograms/kg. Additionally, multiple doses of E2-CDs caused a dose-dependent reduction in body weight at the 10 and 33 micrograms/kg doses with the higher doses causing no further weight reduction. For both single and multiple dosage groups, serum E2 levels remained unchanged after doses of E2-CDS of 10 and 33 micrograms/kg, then increased to 21 pg/ml for the single dosage group and to 23 pg/ml for the multiple dosage group at the 100 micrograms/kg dose, and to 59 pg/ml for singly-injected rats and 60 pg/ml for multiply-injected rats at the 333 micrograms/kg dose. Serum prolactin concentrations were closely correlated with serum E2 levels for both the single and multiple dose groups. These data reveal that a single or multiple doses of E2-CDS can reduce serum LH levels without elevating serum E2 or prolactin concentrations, supporting the concept of brain-enhanced delivery of estradiol with an estradiol chemical delivery system.     

Neuropathy target esterase in hens after sarin and soman

To estimate the potential of small doses of sarin (types I and II) and soman to cause delayed neuropathic effects, 400, 200, 61, and 0 micrograms/kg of sarin-I, 280, 140, 70, and 0 micrograms/kg of sarin-II, and 14.2, 7.1, 3.5, and 0 micrograms/kg of soman by gavage were compared with 510 mg/kg tri-o-cresyl phosphate (TOCP) in 14- to 18-month-old SPF white leghorn hens (4/dose) protected with atropine (100 mg/kg). The neuropathy target esterase (NTE) activity 24 hr after dosing was determined in brain, spinal cord, and lymphocytes and in plasma and brain for cholinesterase and carboxylesterase. None of the compounds showed statistically significant NTE decreases. Sarin-II showed a dose-related trend in the lymphocyte NTE (to 33% of control at 280 micrograms/kg), suggesting that longer exposure to lower doses might cause a cumulative neurotoxic insult. All of the agents decreased the activity of plasma and brain cholinesterase and carboxylesterase. Using more than 70% inhibition of brain NTE as a biochemical predictor of delayed neuropathy, sarin and soman appear unable to cause delayed neuropathy at nonlethal doses within this protocol.     

Daily rhythms of pituitary-ovarian function in the immature hamster are independent of adrenal and pineal influence

In female hamsters, the daily rhythm of LH appeared on the 15th or 16th day after birth with a peak occurring at about 16:00 h (14L:10D, lights on 06:00 h). Progesterone concentrations increased and became rhythmic a few days later. In serum samples collected at 14, 16, 18, 20, 25, 30, 40 and 60-62 days of age between 13:00 and 23:00 h, significant rhythms of serum cortisol and corticosterone concentrations were not detected before 25 days of age; furthermore, the phase of the rhythms did not stabilize to the adult pattern until about 40 days of age. As in the adult, significant rhythms were present in both sexes and the levels of cortisol were greater than those of corticosterone. Injection of pig ACTH (50 i.u./kg body wt, i.p.) significantly increased serum cortisol by 10 days of age, but corticosterone did not respond until 25 days of age. Thus, for cortisol at least, the appearance of 24-h rhythms in the serum is probably not dependent on the ability of the adrenal to respond to ACTH. Ovariectomy had no effect on the late afternoon surge of serum cortisol; similarly, adrenalectomy of immature females did not abolish the surge of LH. Ovariectomy did not alter the daily rhythm of pineal melatonin content and pinealectomy had no effect on the daily afternoon surge of LH. These results demonstrate functional independence of circadian rhythms in the pituitary-gonadal axis and the pituitary-adrenal axis of the immature hamster and also independence of daily rhythms of pineal melatonin and pituitary release of LH.     

Effects of metabolic factors in the diabetic state on the in vitro development of preimplantation mouse embryos

The effects of insulin, glucagon, beta-hydroxybutyrate, and acetoacetate on the in vitro development of preimplantation mouse embryos were studied. In controls, 24% of blastocysts failed to develop successfully when grown for 72 h in Eagle's medium supplemented with 10% fetal calf serum. Insulin at concentrations of 1.0 and 2.0 IU/ml of culture medium interfered with development in 62-63% of the blastocysts. Preimplantation embryos showed a threshold pattern in their reaction to glucagon: its addition in concentrations of 0.0015 mM (5 micrograms/ml) did not significantly inhibit blastocyst development, while concentrations of 0.003 mM (10 micrograms/ml) inhibited 70% of blastocysts. The embryotoxic effects of ketone bodies were manifested only in relatively high doses. beta-hydroxybutyrate was embryotoxic at concentrations greater than 5 mg/ml, and its effects were dose dependent: 48 mM (6 mg/ml) inhibited 45% of blastocysts, while 80 mM (10 mg/ml) arrested 87% of embryos from further development. Acetoacetate at concentrations of 0.1 mM (10 micrograms/ml) inhibited the development of 50% of the blastocysts, and its effects were not dose dependent: concentrations of 1 mM (100 micrograms/ml) inhibited development in 63% of the embryos. The combination of the diabetic metabolic factors in relatively low concentrations was highly embryotoxic, especially when accompanied by hyperglycemia.     

Effect of gamma-aminobutyric acid and muscimol on corticosterone secretion in rats.

The effect of gamma-aminobutyric acid-receptor agonists, GABA and muscimol on the pituitary-adrenocortical activity, measured indirectly through corticosterone secretion, and the receptors involved were investigated in conscious rats. GABA given ip induced a dual effect, in lower dose (10 mg/kg) it significantly decreased the resting serum corticosterone levels while in higher doses (100-500 mg/kg) it considerably raised that level. Muscimol (0.5 mg/kg ip) also increased the corticosterone concentration. Both GABA and muscimol given intracerebroventricularly (icv) induced a significant, dose-related increase in serum corticosterone levels. Bicuculline, a GABAA-receptor antagonist, totally abolished the corticosterone response to GABA but did not influence the response to muscimol. Pretreatment with atropine did not affect the corticosterone response to GABA but significantly diminished the response to muscimol. These results suggest that GABA moderately inhibits the pituitary-adrenal axis at the pituitary level but significantly stimulates it at the hypothalamic level. The stimulatory effect of GABA, but not muscimol, is mediated by hypothalamic GABAA-receptors, and in the effect of muscimol hypothalamic cholinergic, muscarinic receptors are involved to a significant extent.     

The effect of d-fenfluramine on anterior pituitary hormone release in the rat: in vivo and in vitro studies

Administration of d-fenfluramine, a serotonin-releasing drug, to male rats induced a dose-dependent increase in both serum prolactin and corticosterone concentrations. Serum growth hormone levels increased, but not significantly, at a dose of 1.25 mg/kg i.p. and decreased significantly at higher doses. When rats were pretreated with the serotonin uptake inhibitor fluoxetine (10 mg/kg i.p.) 30 min prior to injection of d-fenfluramine (5 mg/kg i.p.), the serum prolactin response to d-fenfluramine was partially inhibited, whereas the growth hormone response was not significantly modified. Fluoxetine pretreatment increased the serum corticosterone to the same level as did d-fenfluramine. d-Fenfluramine's effect on prolactin and growth hormone release was further tested in a hypothalamic-pituitary in vitro system. The addition of d-fenfluramine (5-500 ng/mL) for 30 min to rat hypothalami resulted in an enhancement of prolactin and growth hormone-releasing activities. These were expressed as the ability of the media in which the hypothalami had been incubated to stimulate prolactin and growth hormone release by cultured pituitary cells. The data suggest that the effect of d-fenfluramine on prolactin secretion is exerted through the hypothalamus and is probably mediated, at least partially, by a serotoninergic mechanism. The mechanism of d-fenfluramine's effect on corticosterone and growth hormone release needs further evaluation.     

Glucocorticoid negative feedback and glucocorticoid receptors after hippocampectomy in rats

In rats with dorsal hippocampectomy, glucocorticoid receptors in the hypothalamus and anterior pituitary, as well as the pituitary transcortin-like compound, are preserved, in spite of a 60% depletion of glucocorticoid receptors in the hippocampus. In the hippocampectomized group, basal levels of serum corticosterone (CORT) were increased, although there was a normal response to ether stress. Inhibition of the response to ether with dexamethasone (DEX) was dose-dependent: whereas 100 micrograms/kg completely suppressed serum CORT, 10 micrograms/kg were ineffective. However, we observed a reduced sensitivity to DEX inhibition with 25 micrograms/kg in hippocampectomized animals. These results indicate that the hippocampus is involved in negative feedback mechanisms, although different doses of DEX are needed for this demonstration. The inhibition of serum CORT due to 100 micrograms/kg DEX suggests that negative feedback at sites other than the hippocampus was still operative, in agreement with normal levels of glucocorticoid receptors in the anterior pituitary and hypothalamus of hippocampectomized rats.     

Effects of soman and its antidotes on tracheal mucociliary transport of ferrets

The purpose of this study was to examine the role of acetylcholinesterase on mucociliary transport by use of a potent anticholinesterase agent, soman, and potential antagonists, atropine (muscarinic antagonist) and pralidoxime (acetylcholinesterase reactivator). Initial measurements of mucociliary transport rate were obtained in anesthetized ferrets at 30-min intervals for 5.5 h. These rates remained constant at a mean of 18.2 +/- 1.0 (SE) mm/min. We studied the effects of intravenously administered soman (1-8 micrograms/kg) and observed a dose-related change in the rate of mucociliary transport [-1.1 +/- 2.7 (SE) mm/min after 1 microgram/kg, 9.8 +/- 2.9 mm/min after 5 micrograms/kg, and 14.4 +/- 4.3 mm/min after 8 micrograms/kg of soman]. Pretreatment with atropine completely prevented the response to soman, whereas pretreatment with pralidoxime did not significantly alter the response. We postulate that soman's effect on mucociliary transport relates directly to its cholinergic activity. Failure of pralidoxime to inhibit the effects of soman may relate to pralidoxime's inability to reactivate acetylcholinesterase successfully.     

Effect of the aromatase inhibitor, 4 hydroxyandrostenedione, on the endotoxin-induced changes in steroid hormones in male rats.

The increase in circulating estrogen concentrations that follows injection of Escherichia coli endotoxin (Endo) may be due to increased aromatase activity. We have therefore analysed the effect of the aromatase inhibitor, 4 hydroxyandrostenedione (4OHA) on the steroid hormone response of male rats, particularly the dramatic increase in estrogens and decrease in androgens, induced by Endo. The concentrations of corticosterone (B), progesterone (P4), 17 alpha hydroxyprogesterone (17 alpha OHP4), androstenedione (delta 4), testosterone (T), estrone (E1) and estradiol (E2) were determined 2 hours after injection of increasing doses of 4OHA with and without Endo. The increase in serum estrogen concentrations and drop in serum androgen levels in response to Endo were blocked by a single dose of 4OHA. The effect of 4OHA appeared to be dose dependent. Low doses (30 mg/kg and 50 mg/kg) induced significant changes in the estrogen and androgen responses, but the high dose (100 mg/kg) blocked all changes in sex steroids induced by Endo. 4OHA did not alter the Endo-induced changes in other steroids.     

Effect of oestradiol and tamoxifen on the testosterone response in male rats to a single injection of hCG

A single s.c. injection of hCG (100 i.u.) produced a biphasic serum testosterone response in adult male rats, peaks being noted at 2 h (24 ng/ml) and 3 days (16 ng/ml). The levels fell to control during the intervening interval (8 ng/ml), although there were elevated levels of serum hCG. Maintenance of high oestradiol levels by a s.c. injection of 50 micrograms oestradiol benzoate given on Day 2 after the initial hCG injection failed to prolong the refractory period and the secondary peak of testosterone (16 ng/ml) occurred on Day 3. Administration of the antioestrogen, tamoxifen (2 mg or 3 micrograms), 24 h before or simultaneously with hCG did not prevent testicular refractoriness in vivo because serum testosterone levels still declined after 2 h to reach a nadir at 2 days. The basal in-vitro testosterone production by decapsulated testes from animals injected with hCG was enhanced at 2 h. Stimulation by hCG increased the amount of testosterone produced (X 1.5 that in controls). By 12 h basal production decreased and there was no further increment in testosterone in the presence of hCG. This refractoriness to further hCG stimulation prevailed until Day 3, but the total production of testosterone fell so that at 24 h and 2 days testes were producing basal amounts of testosterone. Testes recovered from refractoriness at 4 and 5 days, when basal and stimulated testosterone production were greater than in controls. Injection of 50 micrograms oestradiol benzoate at 2 days did not prolong the in-vitro refractory period and 2 mg or 3 micrograms tamoxifen had no effect on the in-vitro steroidogenic activity, since testes were still refractory to further hCG stimulation from 12 h to 3 days. The results of the present study do not support the hypothesis that oestradiol is involved in the hCG-induced refractoriness of the Leydig cell. The nadir between the peaks of serum testosterone in vivo corresponds to the period during which the testis is refractory to in-vitro stimulation by hCG.