Disruption of positive- and negative-feature morphine interoceptive occasion setters by dopamine receptor agonism and antagonism in male and female rats

RATIONALE

Internally perceived stimuli evoked by morphine administration can form Pavlovian associations such that they can function as occasion setters (OSs) for externally perceived reward cues in rats, coming to modulate reward-seeking behaviour. Though much research has investigated mechanisms underlying opioid-related reinforcement and analgesia, neurotransmitter systems involved in the functioning of opioids as Pavlovian interoceptive discriminative stimuli remain to be disentangled despite documented differences in the development of tolerance to analgesic versus discriminative stimulus effects.

OBJECTIVES

Dopamine has been implicated in many opioid-related behaviours, so we aimed to investigate the role of this neurotransmitter in expression of morphine occasion setting.

METHODS

Male and female rats were assigned to positive- (FP) or negative-feature (FN) groups and received an injection of morphine or saline before each training session. A 15-s white noise conditioned stimulus (CS) was presented 8 times during every training session; offset of this stimulus was followed by 4-s access to liquid sucrose on morphine, but not saline, sessions for FP rats. FN rats learned the reverse contingency. Following stable discrimination, rats began generalization testing for expression of morphine-guided sucrose seeking after systemic pretreatment with different doses of the non-selective dopamine receptor antagonist, flupenthixol, and the non-selective dopamine receptor agonist, apomorphine, combined with training doses of morphine or saline in a Latin-square design.

RESULTS

The morphine discrimination was acquired under both FP and FN contingencies by males and females. Neither flupenthixol nor apomorphine at any dose substituted for morphine, but both apomorphine and flupenthixol disrupted expression of the morphine OS. This inhibition was specific to sucrose seeking during CS presentations rather than during the period before CS onset and, in the case of apomorphine more so than flupenthixol, to trials on which access to sucrose was anticipated.

CONCLUSIONS

Our findings lend support to a mechanism of occasion setting involving gating of CS-induced dopamine release rather than by direct dopaminergic modulation by the morphine stimulus.

Beyond the Binary: Gender Inclusivity in Schizophrenia Research

Schizophrenia is a severe neuropsychiatric disorder with significant differences in the incidence and symptomology between cisgender men and women. In recent years, considerably more attention has been on the inclusion of sex and gender in schizophrenia research. However, the majority of this research has failed to consider gender outside of the socially constructed binary of men and women. As a result, little is known about schizophrenia in transgender and gender-nonconforming populations. In this review, we present evidence showing that transgender and gender-nonconforming individuals have elevated risk of developing schizophrenia, and we discuss minority stress theory and other potential factors that may contribute to this risk. The need for inclusion of transgender and gender-nonconforming communities in schizophrenia research is emphasized, alongside a discussion on considerations and challenges associated with this type of research. Finally, we offer specific strategies to make research on schizophrenia, and research on other neuropsychiatric disorders, more inclusive of those populations that do not fall within the socially constructed gender binary. If we are to succeed in the development of more personalized therapeutic approaches for all, a better understanding of the variability of the human brain is needed.

Cortical dopamine D5 receptors regulate neuronal circuit oscillatory activity and memory in rats

INTRODUCTION

The dopamine D5 receptor (D5R) shows high expression in cortical regions, yet the role of the receptor in learning and memory remains poorly understood. This study evaluated the impact of prefrontal cortical (PFC) D5R knockdown in rats on learning and memory and assessed the role of the D5R in the regulation of neuronal oscillatory activity and glycogen synthase kinase-3 (GSK-3β), processes integral to cognitive function.

MATERIALS AND METHODS

Using an adeno-associated viral (AAV) vector, male rats were infused with shRNA to the D5R bilaterally into the PFC. Local field potential recordings were taken from freely moving animals and spectral power and coherence were evaluated in, and between, the PFC, orbitofrontal cortex (OFC), hippocampus (HIP), and thalamus. Animals were then assessed in object recognition, object location, and object in place tasks. The activity of PFC GSK-3β, a downstream effector of the D5R, was evaluated.

RESULTS

AAV-mediated knockdown of the D5R in the PFC induced learning and memory deficits. These changes were accompanied by elevations in PFC, OFC, and HIP theta spectral power and PFC-OFC coherence, reduced PFC-thalamus gamma coherence, and increased PFC GSK-3β activity.

CONCLUSION

This work demonstrates a role for PFC D5Rs in the regulation of neuronal oscillatory activity and learning and memory. As elevated GSK-3β activity has been implicated in numerous disorders of cognitive dysfunction, this work also highlights the potential of the D5R as a novel therapeutic target via suppression of GSK-3β.

Addiction-Related Outcomes of Nicotine and Alcohol Co-use: New Insights Following the Rise in Vaping

PURPOSE

Nicotine and alcohol-containing products are some of the most commonly used substances of abuse and are both leading causes of preventable death. These substances also have significant interactions that have additive and, in some cases, multiplicative effects on the health consequences of their use. Thus, to reduce these negative consequences, it is important to understand the abuse liability of nicotine and alcohol in combination, especially in the most relevant use cases among those who are most vulnerable. Specifically, as tobacco cigarette use is continually decreasing, vaping is quickly replacing cigarettes as the primary mode of nicotine use. This pattern is especially true in adolescent populations in which vaping has grown considerably. Particularly concerning is that adolescents are more vulnerable than adults to the negative consequences of substance use. It is therefore imperative to revisit the literature as it relates to the rising state of co-use of vaping products with alcohol. Here, we review the clinical outcomes of nicotine and alcohol co-use as they relate to the abuse liability of each individually. Special attention is paid to adolescent findings, where available, as well as investigations that use nontobacco nicotine products as these may more accurately reflect the more recent trends of co-use.

IMPLICATIONS

Though nicotine alone has previously been considered a proxy for tobacco and tobacco cigarette use, combustible routes of administration have been decreasing. They are, instead, being replaced by e-cigarettes that do not involve other tobacco constituents and contain additional nonnicotine constituents of their own. Unfortunately, the literature remains limited with regard to e-cigarettes and their interactions with other substances, especially their prevalent co-use with alcohol. This review attempts to discuss the current literature on nicotine and alcohol co-use in the context of the vaping epidemic, predominantly focusing on addiction-related outcomes and why e-cigarette use may be unique.

Islet beta cell failure in the 60% pancreatectomised obese hyperlipidaemic Zucker fatty rat: severe dysfunction with altered glycerolipid metabolism without steatosis or a falling beta cell mass

AIMS/HYPOTHESIS

The Zucker fatty (ZF) rat subjected to 60% pancreatectomy (Px) develops moderate diabetes by 3 weeks. We determined whether a progressive fall in beta cell mass and/or beta cell dysfunction contribute to beta cell failure in this type 2 diabetes model.

METHODS

Partial (60%) or sham Px was performed in ZF and Zucker lean (ZL) rats. At 3 weeks post-surgery, beta cell mass and proliferation, proinsulin biosynthesis, pancreatic insulin content, insulin secretion, and islet glucose and lipid metabolism were measured.

RESULTS

ZL-Px rats maintained normal glycaemia and glucose-stimulated insulin secretion (GSIS) despite incomplete recovery of beta cell mass possibly due to compensatory enhanced islet glucose metabolism and lipolysis. ZF-Px rats developed moderate hyperglycaemia (14 mmol/l), hypertriacylglycerolaemia and relative hypoinsulinaemia. Despite beta cell mass recovery and normal arginine-induced insulin secretion, GSIS and pancreatic insulin content were profoundly lowered in ZF-Px rats. Proinsulin biosynthesis was not reduced. Compensatory increases in islet glucose metabolism above those observed in ZF-Sham rats were not seen in ZF-Px rats. Triacylglycerol content was not increased in ZF-Px islets, possibly due to lipodetoxification by enhanced lipolysis and fatty acid oxidation. Fatty acid accumulation into monoacylglycerol and diacylglycerol was increased in ZF-Px islets together with a 4.5-fold elevation in stearoyl-CoA desaturase mRNA expression.

CONCLUSIONS/INTERPRETATION

Falling beta cell mass, reduced proinsulin biosynthesis and islet steatosis are not implicated in early beta cell failure and glucolipotoxicity in ZF-Px rats. Rather, severe beta cell dysfunction with a specific reduction in GSIS and marked depletion of beta cell insulin stores with altered lipid partitioning underlie beta cell failure in this animal model of type 2 diabetes.

Beta cell compensation for insulin resistance in Zucker fatty rats: increased lipolysis and fatty acid signalling

AIMS/HYPOTHESIS

The aim of this study was to determine the role of fatty acid signalling in islet beta cell compensation for insulin resistance in the Zucker fatty fa/fa (ZF) rat, a genetic model of severe obesity, hyperlipidaemia and insulin resistance that does not develop diabetes.

MATERIALS AND METHODS

NEFA augmentation of insulin secretion and fatty acid metabolism were studied in isolated islets from ZF and Zucker lean (ZL) control rats.

RESULTS

Exogenous palmitate markedly potentiated glucose-stimulated insulin secretion (GSIS) in ZF islets, allowing robust secretion at physiological glucose levels (5-8 mmol/l). Exogenous palmitate also synergised with glucagon-like peptide-1 and the cyclic AMP-raising agent forskolin to enhance GSIS in ZF islets only. In assessing islet fatty acid metabolism, we found increased glucose-responsive palmitate esterification and lipolysis processes in ZF islets, suggestive of enhanced triglyceride-fatty acid cycling. Interruption of glucose-stimulated lipolysis by the lipase inhibitor Orlistat (tetrahydrolipstatin) blunted palmitate-augmented GSIS in ZF islets. Fatty acid oxidation was also higher at intermediate glucose levels in ZF islets and steatotic triglyceride accumulation was absent.

CONCLUSIONS/INTERPRETATION

The results highlight the potential importance of NEFA and glucoincretin enhancement of insulin secretion in beta cell compensation for insulin resistance. We propose that coordinated glucose-responsive fatty acid esterification and lipolysis processes, suggestive of triglyceride-fatty acid cycling, play a role in the coupling mechanisms of glucose-induced insulin secretion as well as in beta cell compensation and the hypersecretion of insulin in obesity.

Effects of gestational diabetes on human placental glucose uptake, transfer, and utilisation

AIMS/HYPOTHESIS

Gestational diabetes is associated with complications for the offspring before, during and after delivery. Poor maternal glucose control, however, is a weak predictor of these complications. Given its position at the interface of the maternal and fetal circulations, the placenta possibly plays a crucial part in protecting the fetus from adverse effects from the maternal diabetic milieu. We hypothesised that gestational diabetes may result in changes in placental function, particularly with respect to the uptake, transfer, and/or utilisation of glucose. We aimed to examine glucose transport and utilisation in intact human placental lobules from women with gestational diabetes and those from normal pregnancies.

METHOD

Dual perfusion of an isolated placental lobule was done on placentae from diet treated gestational diabetic (n = 7) and normal pregnant patients (n = 9) using maternal glucose concentrations of 4, 8, 16 and 24 mmol/l in random order over a 4-h experiment. Results were expressed in micromol x min(-1) x g(-1).

RESULTS

D-glucose uptake from the maternal circulation (control 0.492 vs gestational diabetes mellitus 0.248, at 8 mmol/l maternal glucose), D-glucose utilisation by the placenta (0.255 vs 0.129), D-glucose transfer to the fetal circulation (direct 0.979 vs 0.402; net transfer 0.269 vs 0.118) and L-lactate maternal release into both the fetal (0.052 vs 0.042) and maternal (0.255 vs 0.129) circulation were significantly reduced during in vitro perfusion of placentae from patients with gestational diabetic pregnancies. Transfer of 3H-L-glucose also significantly reduced in the diabetic group (8.1% vs 2.6%).

CONCLUSION/INTERPRETATION

These results suggest that placental transport and metabolism of D-glucose is altered during gestational diabetes.

In vitro 2,3,7,8-tetrachlorodibenzo-p-dioxin interference with the anterior pituitary hormone adrenocorticortropin

Treatment of male Sprague-Dawley rats with a single oral dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been shown to increase serum adrenocorticotropin (ACTH) and decrease serum corticosterone. The present in vitro study was designed to assess whether TCDD has a direct effect on the anterior pituitary under basal and stimulated conditions. Primary anterior pituitary cell cultures were prepared from normal 180- to 220-g male Sprague-Dawley rats and the cultures treated with 10(-9)-10(-19) M TCDD. Maximal secretion of ACTH occurred between 10(-11) and 10(-15) M TCDD for both medium (2-fold) and intracellular (1.5-fold) concentrations after 24 h TCDD exposure. TCDD treatment also caused an early (6 h) and persistent (10 days) increase in basal medium (1.4- to 2.8-fold) and intracellular (1.1- to 1.7-fold) ACTH concentrations. However, while stimulation with corticotropin-releasing hormone (CRH) increased intracellular ACTH 1.5- to 1.7-fold in pituitary cells treated for 24 h with 10(-9)-10(-13) M TCDD, ACTH secreted into the media was decreased by 30-50% compared with controls. Lastly, the secretagogue arginine-8-vaso-pressin (AVP), did not increase the amount of ACTH secreted above levels observed with basal TCDD exposure. From this study, it appears that TCDD stimulates in vitro synthesis and secretion of ACTH by the anterior pituitary under basal conditions, but decreases the pituitary's responsiveness to CRH and AVP stimulation.

The set point for maternal glucose homeostasis is lowered during late pregnancy in the rat: the role of the islet beta-cell and liver

The aim of this study was to determine the effects of late pregnancy on the ability of insulin to suppress maternal hepatic glucose production in the rat. Unlike in most previous studies, suppression of hepatic glucose production was measured at levels of glycaemia above the relatively hypoglycaemic basal pregnant level. Glucose kinetics were measured using steady-state tracer methodology in chronically catheterised, conscious virgin control and pregnant rats, firstly, during basal and low-dose hyperinsulinaemic euglycaemic clamp conditions and secondly, during a three-step glucose infusion protocol (glucose infusion rates of 0, 60 and 150 mumol.kg-1. min-1). During the clamps, plasma glucose levels were not different (6.1 +/- 0.4 vs 6.5 +/- 0.3 mmol/l, pregnant vs virgin; N.S.), but plasma insulin levels were higher in the pregnant rats (242 +/- 30 vs 154 +/- 18 pmol/l. pregnant vs virgin; p < 0.05) most probably due to stimulated endogenous insulin release in this group. Hepatic glucose production was suppressed from basal levels by 41% in virgin and 90% in pregnant rats. During the glucose infusion studies, at matched insulin levels (147 +/- 10 vs 152 +/- 14 pmol/l), but at plasma glucose levels which were much lower in the pregnant rats (5.5 +/- 0.2 vs 8.4 +/- 0.6 mmol/l, pregnant vs virgin; p < 0.0001), hepatic glucose production was shown to be suppressed by a similar degree in both groups (41 +/- 5 vs 51 +/- 5% from basal, pregnant vs virgin; N.S.). Both the plasma insulin and percentage suppression of hepatic glucose production dose responses to plasma glucose were markedly shifted to the left indicating that the plasma glucose set point is lowered in pregnancy. In conclusion, suppression of hepatic glucose production by insulin is not impaired and the set point for plasma glucose homeostasis is lowered during late pregnancy in the rat.

Maternal serum triglyceride, glucose tolerance, and neonatal birth weight ratio in pregnancy

OBJECTIVE

To determine the value of measuring serum triglyceride (TG) levels early in pregnancy for predicting late-gestation glucose tolerance and neonatal birth weight ratio (BWR) (birth weight corrected for gestational age).

RESEARCH DESIGN AND METHODS

The relationships between morning nonfasting TG measured early in pregnancy (gestational age 12 +/- 6 weeks [mean +/- SD]) and glucose tolerance measured by a 3-h 50-g oral glucose tolerance test (OGTT) late in pregnancy (gestational age 30 +/- 3 weeks) and BWR were investigated in 388 women attending routine antenatal care. The data were analyzed for all women in addition to subgroups of Australian/Western European-born (n = 246) and Asian-born (n = 97) women.

RESULTS

Morning nonfasting TG positively correlated with the OGTT glucose area under the curve (OGTT-GAUC) (r = 0.23, P < 0.0001) in all subjects. This correlation was stronger in the subset of subjects who had TG measured between 9 and 12 weeks of gestation (r = 0.35, P = 0.0001) and was particularly strong in Asian-born women who had TG measured within this period (r = 0.71, P < 0.0001). Mean TG and the 2- and 3-h OGTT values were higher in Asian-born subjects compared with Australian/Western European-born subjects (P = 0.004, P < 0.0001, and P = 0.02, respectively). TG correlated positively with BWR in all subjects (r = 0.12, P = 0.02), in Asian-born subjects (r = 0.23, P = 0.02), and in subjects with gestational diabetes mellitus (GDM) (r = 0.60, P = < 0.001).

CONCLUSIONS

TG, if measured between 9 and 12 weeks of gestation, has moderate predictive value for subsequent glucose tolerance in pregnancy. TG is also predictive of BWR in GDM subjects. Further studies are warranted to investigate the role of early TG measurement in the screening and management of GDM. Metabolic heterogeneity exists between Asian-born and Australian/Western European-born women, the significance of which is still unclear and warrants further study.

The feto-placental glucose steal phenomenon is a major cause of maternal metabolic adaptation during late pregnancy in the rat

The aim of this study was to determine the extent to which a feto-placental glucose steal phenomenon contributes to the process of maternal metabolic adaptation to late pregnancy. Glucose metabolism was studied in virgin control, pregnant rats and virgin rats with a phlorizin-induced model of the feto-placental glucose steal phenomenon. Whole body glucose kinetics and glucose uptake into individual tissues were measured in anaesthetised rats basally and during hyperinsulinaemic euglycaemic clamps. The basal glucose metabolism of the pregnant rats was closely mimicked by the phlorizin-treated rats. Basal plasma glucose was 39% and 38% lower (p < 0.0001 for both); hepatic glucose production was 21% and 26% higher (p < 0.05 for both); and plasma glucose clearance was 109% and 104% higher (p < 0.0001 for both) in the pregnant and phlorizin-treated rats, respectively, compared to the control rats. Basal glucose uptake into peripheral tissues was lower in both the pregnant and phlorizin-treated compared to the control rats, being most evident in heart (p < 0.01 for both) and brown adipose tissue (p < 0.001 for both). In the clamp studies, impairment of glucose uptake into skeletal muscle was observed in both the pregnant and phlorizin-treated rats compared to the control rats. In conclusion, the feto-placental glucose steal phenomenon is a major contributing factor to postabsorptive glucose metabolism in late pregnancy. This phenomenon also contributes to the impairment of maternal insulin-stimulated peripheral glucose uptake.

Clinical and histological correlations of decline in renal function in diabetic patients with proteinuria

In 47 patients with diabetic nephropathy (29 type I, 18 type II) renal function and blood pressure (BP) (treated with or without an angiotensin-converting enzyme [ACE] inhibitor, enalapril [10 mg], in 38 hypertensive patients) were followed over 4 years. A percutaneous renal biopsy was performed in all patients initially and repeated in a representative 19 patients with treated hypertension after 4 years. Mean glomerular volume (MGV), interstitial fibrosis (IF), capillary volume, and sclerosed glomeruli (GS) were measured histomorphometrically. Mean fall in creatinine clearance (CCr) was 11.8% after 4 years with no difference between treatment groups or type of diabetes. BP both initially and during treatment correlated with initial and final serum creatinine and CCr (P < 0.01). There were no histomorphometric differences between type I and type II patients or hypertension treatment groups. Initial IF correlated with initial and final serum creatinine and CCr (P < 0.05) in all patients and type I patients alone, MGV correlated inversely with CCr in type I patients (P < 0.05). After 4 years, IF (24.8 vs. 30.0%, P < 0.01) and GS (26 vs. 37%, P < 0.05) increased significantly, and increase in IF correlated with fall in CCr (P < 0.01). Proteinuria and HbA1 did not correlate with indexes of function or structure. In this longitudinal study of patients with diabetic nephropathy, there was a close relation between BP and renal function but no difference between treatment with enalapril and other hypertensive agents. The correlations between renal function and histology at entry and after 4 years suggest that IF is a co-determinant of renal function in diabetic nephropathy.

TCDD alters pituitary-adrenal function. II: Evidence for decreased bioactivity of ACTH

The present study assessed the ability of primary cultures of rat anterior pituitary cells to secrete bioactive ACTH in the presence of 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD). The bioactivity of the secreted pituitary cell ACTH was determined by its ability to stimulate secretion of corticosterone from primary cultures of rat adrenal cells. ACTH from basal or CRH stimulated pituitary cells treated with TCDD was found to be less capable of stimulating corticosterone secretion from primary rat adrenal cell cultures than equimolar concentrations of ACTH purchased from a commercial supplier. Corticosterone secretion from adrenal cell cultures treated with ACTH from basal or CRH stimulated pituitary cell cultures exposed to TCDD was decreased by 60 and 70%, respectively. The decreased ability to stimulate corticosterone secretion can be overcome when extracts of ACTH from pituitary cell cultures treated with TCDD are supplemented with commercial ACTH. These findings indicate that TCDD may alter the bioactivity of secreted ACTH from the anterior pituitary gland.

TCDD alters pituitary-adrenal function. I: Adrenal responsiveness to exogenous ACTH

Plasma ACTH concentrations in 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD)-treated rats (50 micrograms/kg; single, oral dose) were 2.1-, 2.1-, 2.9-, 1.7-, 1.5-, 2.0- and 3.0-fold greater than control values, respectively, at days 1, 3, 5, 7, 10, and 14. At days 1 and 5 plasma corticosterone concentrations were increased 5.1- and 8.0-fold, respectively; whereas, at days 10 and 14 they were depressed to values of 50% and 39% of controls, respectively. Adrenal glands were excised from rats treated with TCDD and corticosterone production was assessed. Basal corticosterone concentrations produced by treated adrenals were depressed to 81%, 72%, and 71% of control values at days 5, 7, and 14, respectively. Corticosterone secretion by ACTH stimulated adrenals was equivalent to controls. These findings suggest that TCDD exposure decreases the bioactivity of the ACTH secreted by the anterior pituitary.

Tetrachlorodibenzo-p-dioxin alters rat hypothalamic endorphin and mu opioid receptors

The present study was undertaken to assess if hypothalamic beta-endorphin (beta E) and/or brain mu opioid receptors are associated with 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) (50 micrograms/kg)-induced hypophagia and body weight decline in rats. Hypothalamic beta E concentrations were initially increased to 166% of controls on day 1, and then were depressed to 39% and 49% of control values on days 2 and 3, respectively. Brain mu opioid receptor number was increased 60% in TCDD-treated rats at day 3 without a change in the binding affinity. Food-restricted rats did not exhibit changes in hypothalamic beta E concentrations or brain mu opioid receptor number. These results indicate that TCDD causes early perturbations in hypothalamic beta E concentrations and brain mu receptor number, which may contribute to the mechanisms by which TCDD leads to decreased food intake and progressive weight loss.

Human chorionic gonadotropin treatment prevents depressed 17 alpha-hydroxylase/C17-20 lyase activities and serum testosterone concentrations in 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated rats

It is known that administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) causes decreased serum testosterone concentrations in the rat. Previous studies in this laboratory have shown that in rats TCDD exposure results in decreased 17 alpha-hydroxylase and C17-20 lyase activities. The decreases in these activities paralleled decreases in testicular microsomal heme and cytochrome P450 contents. As reported herein, neither testicular mitochondrial cytochrome P450 content nor the activity of cholesterol side-chain cleavage was altered in rats exposed to TCDD. Since the production of testosterone in the testis is dependent on LH, it is important to determine the early effects of TCDD on serum LH concentrations in the rat. Male Sprague-Dawley rats were given a single, oral dose of TCDD (50 micrograms/kg). Serum LH concentrations were determined by RIA on Days 1, 2, 3, 5, and 7 following TCDD treatment. Rat serum LH concentrations were decreased to 60% of controls as early as Day 1 and continued to be depressed on Days 2 and 3 at 53% and 59% of control values, respectively. Rat serum LH returned to control values by Day 5 in spite of continued depression of serum testosterone concentrations. The early depression in serum LH levels caused by TCDD may be related to the subsequent androgenic deficiency in the rat. Treatment of rats with hCG was found to be able to prevent the depression of the activities of testicular microsomal 17 alpha-hydroxylase and C17-20 lyase and serum testosterone concentrations caused by TCDD. These data indicate that TCDD decreases serum testosterone by decreasing P450(17 alpha) and C17-20 but not P450sec activities and that hCG treatment prevents the TCDD-induced decrease.

Chronic ethanol consumption depresses hypothalamic-pituitary-adrenal function in aged rats

In separate experiments, nine (n = 20) and fifteen (n = 12) month old rats were treated with either 6% ethanol or 12% sucrose (to balance caloric intake) in the drinking water to examine the effect of chronic ethanol consumption on the hypothalamic-pituitary-adrenal axis of aged rats. Rats were maintained on these treatment regimens for thirty days and were killed by decapitation. Blood was collected and plasma concentrations of adrenocorticotropin (ACTH) and corticosterone were determined by radioimmunoassay. Adrenal glands were cleaned, quartered and used to test in vitro responsiveness to ACTH. Anterior pituitary glands from all 15 month old rats and one half of the nine month old rats were collected, frozen and extracted for measurement of tissue ACTH concentration. The remaining anterior pituitary glands from the nine month old rats were challenged with corticotropin releasing hormone (CRH) to test in vitro responsiveness. In nine month old rats, chronic ethanol consumption decreased plasma ACTH and corticosterone (P less than 0.05). Pituitary ACTH concentrations were unchanged in treated nine month old rats, but the amount of pituitary ACTH released in response to CRH was decreased (P less than 0.05) in rats consuming ethanol. In vitro responsiveness of the adrenal gland to ACTH in nine month old rats consuming ethanol was unchanged (P greater than 0.05). Plasma ACTH and corticosterone concentrations were also decreased in 15 month old rats chronically consuming ethanol (P less than 0.05). No differences were noted in responsiveness of the adrenal gland or in the amount of pituitary ACTH due to ethanol consumption in 15 month old rats (P greater than 0.05). The results of these experiments indicate that chronic ethanol consumption decreases hypothalamic-pituitary-adrenal function in aged rats.

Genotype at the P450scc locus determines differences in the amount of P450scc protein and maximal testosterone production in mouse Leydig cells

A genetic difference in maximal testosterone production in Leydig cells relates to differences in the genotype at the P450scc locus. The genetic relationship between the P450scc gene, the amount of Leydig cell P450scc protein, and maximal testosterone production was determined in the F2 generation of mice derived from SWR/J mice (SWR), a high Leydig cell testosterone-producing strain, and from C3H/HeJ (C3H), a low Leydig cell testosterone-producing strain. A restriction fragment length polymorphism was identified in the P450scc gene between SWR and C3H mice. This restriction fragment length polymorphism was used to identify F2 mice homozygous for the SWR or the C3H alleles of the P450scc gene. The two types of homozygous mice were compared with regard to maximal testosterone production and the amounts of P450scc, P45017 alpha, and 3 beta-hydroxysteroid dehydrogenase isomerase (3 beta HSD) proteins. Maximal testosterone production, amounts of P450scc and 3 beta HSD were significantly greater in the SWR than in the C3H progenitor mice. In the F2 mice, homozygous for either the SWR or the C3H allele of P450scc, the differences in maximal testosterone production and the amount of P450scc protein were comparable to the differences in the two progenitor strains. A significant correlation (r = 0.75; P less than 0.01) was found between the amount of P450scc protein and maximal testosterone production. No differences in the amounts of P45017 alpha or 3 beta HSD were observed in the F2 males.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of dietary energy intake on prepubertal development of Brahman bulls

Twelve Brahman bulls (paired by sire, weight and age) were assigned randomly and limit fed to gain either .10 to .25 (moderate gain; MG) or .75 to 1.0 (high gain: HG) kg.hd-1.d-1 to examine the effect of dietary energy on onset of puberty. Hip height (HH), scrotal circumference (SC) and serum samples (20 min for 6 h) were obtained at four times (AGE): 0, 56 and 112 d on feed and after appearance of first motile spermatozoa (FS) in the ejaculate of HG bull of the pair. At FS both bulls of a pair were slaughtered, reproductive tissues were collected and in vitro GnRH release from the median eminence (ME) was measured. Increases in BW, HH and SC were greater (P less than .05) in HG bulls. Basal ME GnRH secretion was greater (P less than .05) in HG bulls. Serum LH concentrations were unchanged by energy level (P greater than .10) but increased (P less than .01) with increasing AGE. AGE and energy level increased (P less than .01) basal, mean and total serum testosterone (T) and these two factors acted synergistically (P less than .01). Height and amplitude of T pulses were increased by energy level (P less than .003) and AGE (P less than .002). Testicular T (P less than .08) and development (P less than .05) were increased in HG bulls. Growth hormone peak height and amplitude concentrations following feeding increased with AGE (P less than .06) but were not altered (P greater than .10) by energy level. Serum triglycerides (P less than .03) and BUN (P less than .003) increased with increasing AGE (P greater than .01). These data indicate that dietary energy level influences onset of puberty most directly at the testicular level.

Postpartum reproduction in protein restricted beef cows: effect on the hypothalamic-pituitary-ovarian axis

The influence of dietary CP on circulating LH and anterior pituitary and hypothalamic function was examined. In Exp. 1, 28 cows were randomly assigned to four treatment groups: adequate CP (ADQ; .96 kg/d) or deficient CP (DEF; .32 kg/d) beginning at 90, 60 and 30 d before parturition and continued at a 33% increase in feed consumption after parturition. Cows were bled at 15-min intervals for 8 h on d 20, 40 and 60 after parturition. Pituitaries were collected on d 62 to analyze GnRH receptor numbers and gonadotropin content. Frequency of pulsatile LH release increased (P less than .05) from 20 to 60 d in ADQ cows. Basal and mean LH were not affected (P greater than .10) by CP restriction or by days after parturition. Crude protein did not affect pituitary GnRH receptors (P greater than .10), but it did affect pituitary LH content, FSH content and FSH concentration (P less than .05). In Exp. 2, 28 cows were assigned to treatment groups as in Exp. 1. All cows were challenged with GnRH (.22 micrograms/kg BW) at 20, 40 and 60 d after parturition and were bled every 30 min for 6 h. Responsiveness to GnRH increased with increased time after parturition (P less than .07). Deficient CP decreased GnRH-induced LH release (P less than .05). In Exp. 3, 12 cows were randomly assigned to ADQ or DEF CP beginning 120 d before parturition. All cows received 1 mg estradiol-17 beta (E2) on d 19, 39 and 59 after parturition and were bled every 30 min for 14 h beginning 14 h following E2. Response to E2 was unaffected by CP restriction (P greater than .10), whereas time to E2-induced LH peak decreased as time after parturition increased in ADQ cows (P less than .05). Results suggest that delayed return to estrus in CP-deficient postpartum beef cows might be due to reduced gonadotropin release from the anterior pituitary and decreased anterior pituitary responsiveness to GnRH.

Improved glucose tolerance in gestational diabetic women on a low fat, high unrefined carbohydrate diet

In a randomized cross-over study 5 gestational diabetic women were tested on a low fat, high unrefined carbohydrate (HC) diet and a low carbohydrate (LC) diet for a period of 4 days each. Glucose tolerance was shown to be significantly improved on the HC diet compared to the LC diet (p less than 0.05). Urinary glucose output was 50% lower on the HC diet (1.3 +/- 1.1 mmol/d) than on the LC diet (2.6 +/- 3.0 mmol/d), although this difference was not statistically significant. Fasting free fatty acid levels were significantly lower on the HC diet (HC 590 +/- 270 mumol/l, LC 690 +/- 270 mumol/l; p less than 0.02); as were the fasting cholesterol levels (HC 5.9 +/- 1.1 mmol/l, LC 6.3 +/- 1.1 mmol/l; p less than 0.01). Fasting plasma glucose, 2 h postprandial plasma glucose, and fasting plasma triglyceride levels did not differ on the 2 diets. These pilot study results suggest that diets low in fat and high in unrefined carbohydrate content are beneficial to the management of women with gestational diabetes.

The effects of heat stress on the development of the foetal lamb

Environmental heat stress in tropical sheep suppressed lamb birth weight, but the animals which did not experience hyperthermia under natural environmental conditions gave birth to significantly heavicr (P<0.01) lambs than their less adapted counterparts. Climate chamber studies designed to simulate the rectal temperature patterns of tropical sheep demonstrated that, without nutritional intervention, heat stress during the last month of pregnancy significantly retarded foetal growth (birth weight 2.3 kg v. 3.4 kg; P< 0.01) and maturation of wool follicles (P< 0.01). By comparison, severe nutritional restrictions during the last 3 months of pregnancy also caused a significant reduction in lamb birth weight (3.2 kg v. 3.9 kg; P<O.01), but this difference was not so marked.