R.A. Siegel

In vitro conversion of pregnenolone to progesterone by discrete brain areas of the male rat

[7-3H]-Pregnenolone was incubated with homogenates of discrete limbic brain areas from male rats, in the presence of NAD, and its conversion to [7-3H]-progesterone was quantitatively determined. The highest conversion occurred in amygdalar tissue, followed by septum. Lower conversion occurred in hippocampus and hypothalamus, while no significant conversion could be detected in cerebral cortical tissue. These results demonstrate the presence of 3β-hydroxysteroid oxidoreductase, 5-ene-isomerase in the male rat limbic brain. The possible physiological significance of this presence is discussed.

Hippocampal cell nuclear binding of corticosterone following 5,7-dihydroxytryptamine ☆

Adult male rats were injected into the lateral brain ventricle with 5,7-dihydroxytryptamine (5,7-DHT). They were adrenalectomized 5-7 days later and, following an additional 24 h, the specific in vitro [3H]corticosterone binding capacity of dorsal hippocampal slices was determined by estimation of uptake of radioactivity by the nuclear fraction. Specific corticosterone (CS) binding was reduced by 50-70% in the neurotoxin-treated as compared to vehicle-injected animals. Brain serotonin and 5-hydroxyindoleacetic acid concentrations were depleted by 50-70% in the 5,7-DHT-injected rats. These results suggest that the maintenance of normal dorsal hippocampal CS binding capacity is dependent upon the integrity of endogenous brain serotoninergic neuronal systems.

Effects of naloxone on basal and stress-induced prolactin secretion, in intact, hypothalamic deafferentated, adrenalectomized, and dexamethasone-pretreated male rats.

The effects of naloxone (Na1) on basal and stress-induced PRL secretion were investigated in intact (N) adult male rats, as were its effects in rats with complete hypothalamic deafferentation (CHD), in adrenalectomized (adrenX) rats, and in rats pretreated with dexamethasone (dex). Forty-five minutes subsequent to Na1 administration (5 mg/kg, BW, IP) basal serum levels of PRL were reduced by approximately 25% (p less than 0.05), in both N and CHD groups. PRL secretory responses to acute exposure to both photic and acoustic stress wee markedly attenuated in Na1-injected, as compared to vehicle-injected animals. Basal serum PRL concentrations were elevated by 40% in adrenX rats (p less than 0.05), as reduced by 25% (p less than 0.05) in dex-treated rats, as compared to controls. In both these experimental groups, Na1 administration caused significant reductions in serum PRL. This study demonstrates that stress-induced, as well as basal PRL secretion, is attenuated by Na1, and points to a hypothalamic site of action in this regard. Furthermore, these Na1 effects are independent of glucocorticoid interactions with the CNS.

Effects of Systemically Administered Indomethacin on Basal and Stress-Induced ACTH and Corticosterone Secretion in the Male Rat

The effects of the prostaglandin (PG) synthetase inhibitor indomethacin (IM) on basal and stress-induced activity of the hypothalamo-hypophyseal-adrenal (HHA) axis were investigated. IM was systemically administered to adult male rats in a single injection (5 mg/100 g BW s.c.). The animals were sacrificed 24 h later, either under basal conditions, or following 30 min exposure to environmental temperature of 36 degrees C. Serum ACTH and corticosterone (CS) were determined by RIA and CBG, respectively, and hypothalamic and adenohypophyseal PGE2 and total PGE concentrations were estimated by RIA. IM treatment resulted in elevated basal levels of both hormones. Heat exposure led to elevated serum ACTH and CS concentrations in both vehicle- and IM-treated groups, with the ACTH heat response in IM-treated animals being greater than that observed in controls. PGE2, and PGE1 plus PGE2 concentrations were markedly reduced in both hypothalamic and adenohypophyseal tissues, following IM treatment. This study demonstrates that simultaneous reductions in hypothalamic and adenohypophyseal PG concentrations are compatible with hyperactivity of the HHA axis.

ACTH and Corticosterone Secretion Following Indomethacin, in Intact, Adrenalectomized and Dexamethasone-Pretreated Male Rats

The present study was designed to determine the role of glucocorticoids in the mediation of the stimulatory effect of indomethacin (IM) on the hypothalamo-hypophyseal-adrenal axis. Intact male rats were treated with a single injection of either dexamethasone (Dex; 20 micrograms/100 g body weight), IM (5 mg/100 g body weight), or IM + Dex or their respective vehicles. In Dex-treated rats, ACTH and corticosterone (CS) were significantly reduced over a period of 20 h as compared to the vehicle-treated group. As we have previously demonstrated, injection of IM markedly elevated serum ACTH and CS for at least 20 h. Administration of Dex 2 h prior to IM treatment delayed the stimulatory effect of IM for 5 h; subsequently, however, Dex was without effect. In adrenalectomized rats, ether stress elicited a marked rise in serum ACTH levels. On the contrary, IM was completely ineffective in these rats. These studies suggest that the mode of action of IM in causing hypersecretion of ACTH and CS is by interfering with the negative feedback effects of the glucocorticoids.

ACTH and corticosterone secretion following 2-deoxyglucose administration in intact and in hypothalamic deafferentated male rats.

Adult male rats were given a single i.p. injection of 2-deoxyglucose (2-DG, 100-400 mg/kg b. wt). The animals were decapitated 1-4 h later and trunk blood was collected for ACTH, corticosterone (CS) and glucose determinations. Serum ACTH and CS were markedly elevated when compared with saline-treated animals; these elevations were correlated with given doses of 2-DG so that with the higher dose, an approximately 6-fold increase in serum levels of both hormones was observed. Injection of 2-DG up to 200 mg/kg did not change serum glucose levels; injection of 400 mg/kg of 2-DG increased serum glucose by approximately 2-fold. A time course study showed that levels of serum ACTH, CS and glucose were maximal 1 h after 2-DG administration and returned to basal values 3 h later. Injection of 2-DG to animals with complete hypothalamic deafferentation failed to induce any change in serum ACTH, CS or glucose. This study demonstrates that: (1) 2-DG can stimulate the hypothalamo-hypophyseal-adrenal (HHA) axis as measured by ACTH and CS; this effect is not related to blood glucose levels; (2) the HHA response to 2-DG is mediated by sites outside the mediobasal hypothalamus.

In vitro metabolism of cortisol by human abdominal adipose tissue

[1,2-3H]-cortisol was incubated with homogenates of abdominal subcutaneous adipose tissue obtained from non-obese and obese female patients. In the presence of NAD or NADP 15-18% of the substrate was converted to cortisone: no other products could be detected. No cortisol metabolism could be detected upon the addition of NADH or NADPH. Kinetic studies of the dependency of cortisone formation upon incubation time, tissue and substrate concentrations showed that 11 beta-hydroxy steroid dehydrogenase activity in homogenates of adipose tissue if taken from the non-obese and obese patients is similar. The possible significance of 11 beta-hydroxy steroid dehydrogenase activity in adipose tissue is discussed.

A temporal study of post-adrenalectomy increase in ACTH secretion in the rat: effect of various hypothalamic deafferentations.

Adult male rats, intact (N) or with complete (CHD), anterior (AHD), or posterior (PHD) hypothalamic deafferentations were bilaterally adrenalectomized. At 3, 6, 12 and 20 days post-adrenalectomy they were decapitated and trunk blood was collected for ACTH determinations. In N rats, ACTH markedly elevated up to 850 pg/ml. A similar ACTH response was found in PHD rats but the values were lower by approximately 20%. In contrast, in either AHD or CHD rats, ACTH responses were markedly attenuated and reached a plateau of about 350 pg/ml. These data suggest that: (1) neural inputs entering the medio-basal hypothalamus (MBH) from both the caudal and rostral directions are important for obtaining maximal ACTH responses following adrenalectomy; (2) at least part of this ACTH response is mediated by sites inside the MBH or in the pituitary.

CORRECTION BY BROMOCRIPTINE OF HYPOTHALAMIC DYSFUNCTION AND POST-PRANDIAL HYPOGLYCAEMIC SYMPTOMS IN A 31-YEAR-OLD WOMAN

A 31‐year old female presented with recurrent episodes of post‐prandial hypoglycaemic symptoms. Basal serum levels of ACTH, cortisol, GH, insulin and glucagon were normal. An adrenaline test demonstrated a normal peripheral response. An exercise test failed to produce ACTH, cortisol or FFA responses. Insulin (0·1 u/kg)‐induced‐hypoglycaemia failed to elevate serum ACTH, cortisol or GH. Metyrapone and ACTH tests were normal, demonstrating adequate hypophyseal and adrenal function. These findings suggested that the patient suffered from hypothalamic dysfunction. Brornocriptine (Parlodel, 7·5 mg/d for 5 weeks) resulted in an improved general condition, accompanied by a decrease in sugar consumption. Following treatment, FFA, ACTH and cortisol responses to exercise test were normal, as were ACTH, cortisol and GH responses to insulin‐induced hypoglycaemia. It is concluded that bromocriptine may be useful in the treatment of post‐prandial hypoglycaemic symptoms associated with hypothalamic dysfunction.