Alexander C. Brownie

The in vivo effect of indomethacin and prostaglandin E2 on acth and Dbcamp-induced steroidogenesis in hypophysectomized rats

Abstract The level of plasma corticosterone attained in hypophysectomized rats stimulated with ACTH was significantly reduced by pretreatment with indomethacin, an inhibitor of prostaglandin synthesis. This effect was not seen in animals stimulated with dibutyryl cyclic AMP. Intraperitoneal injection of prostaglandin E2 to indomethacin treated rats restored the normal response to ACTH stimulation. However, PGE2 itself did not have any significant effect on plasma corticosterone levels. These findings suggest that prostaglandins are involved, perhaps in an allosteric fashion, in the mechanism of action of ACTH.

Pathways for androgen biosynthesis in monkey testis

Abstract Monkey testicular homogenates and minces were incubated for varying lengths of time with pairs of differentially labelled steroids, progesterone and pregnenolone, 17α-hydroxyprogesterone and 17α-hydroxypregnenolone and androstenedione and dehydroepiandrosterone, in order to elucidate the possible pathways involved in testosterone biosynthesis. It was evident that all these steroids could be converted to testosterone but pregnenolone and 17α-hydroxy-pregnenolone were better precursors than progesterone and 17α-hydroxypro-gesterone. The results suggest that testosterone is made from pregnenolone and 17α-hydroxypregnenolone by a pathway independent of androstenedione. Δ 5 -Androstenediol must be considered as a possible intermediate in testosterone biosynthesis having been formed from both pregnenolone and 17α-hydroxypreg-nenolone.

The metabolism of progesterone-4-14C by adrenal homogenates from rats with adrenal-regeneration hypertension(1)

Abstract Progesterone-4- 14 C has been incubated with homogenates prepared from intact and regenerating rat adrenals. While corticosterone- 14 C was the major metabolite from incubations with intact adrenals, both corticosterone- 14 C and 11-deoxy-corticosterone- 14 C were identified as major metabolites from incubations of regenerating adrenals. 11-Deoxycorticosterone secretion by regenerating adrenals might explain the development of adrenal-regeneration hypertension.

Serum 11-deoxycorticosterone levels in adrenal-regeneration hypertension under conditions of quiescence and stress

A time course study to measure adrenal cortical function was undertaken for the period prior to the development of hypertension until the onset of hypertension in the adrenal-regeneration hypertension (ARH) model. Quiescent rat kills were used so that all adrenal cortical parameters investigated would reflect basal or resting levels for controls. Thus a more accurate determination of the differences between control and experimental animals could be made. A radioimmunoassay procedure for deoxycorticosterone was developed to measure this steroid in individual rat serum samples. Elevated serum deoxycorticosterone levels were observed in rats with regenerating adrenals when they were killed under quiescent conditions. This agreed with our recently reported in vitro finding of restoration of cholesterol side chain cleavage activity while 11beta-hydroxylase activity remained imparied 25 days after adrenal enucleation. When rats were killed after ether stress, deoxycorticosterone levels were elevated in both control rats and in rats with regenerating adrenals but the difference was not significant. In contrast, after ether stress serum corticosterone levels were lower in rats with regenerating adrenals than in controls. These studies, in conjunction with our previous in vitro findings, point to the importance of deoxycorticosterone in the pathogenesis of adrenal regeneration hypertension and help to explain the anomalous corticosteroid secretion rate data found in this experimental hypertension model.

Failure of ACTH to mimic the stress-induced activation of rat adrenocortical cholesterol ester hydrolase in vivo

Abstract Rat adrenocortical cholesterol ester hydrolase activity does not respond to the circadian rhythm of the pituitary-adrenal axis under quiescent conditions. However, stress activates this enzyme, producing a greater increase in activity at the high point of the cycle than at the low point. This stress-induced effect requires the presence of the pituitary. It is not mimicked by administration of exogenous porcine ACTH to either hypophysectomized or dexamethasone-suppressed rats, but homogenates of whole rat pituitary tissue do possess substantial stimulatory capacity.

Gamma3-melanotropin promotes mitochondrial cholesterol accumulation in the rat adrenal cortex

Abstract Gamma 3-melanotropin (γ3-MSH) facilitates a rapid, dose-dependent, and cycloheximide-insensitive increase in the concentration of mitochondrial free cholesterol in the adrenals of hypophysectomized rats. Physiological concentrations of various synthetic and native preparations of γ3-MSH are potent, while γ-MSH is not. This cholesterol accumulation coincides with the activation of cholesteryl ester hydrolysis by γ3-MSH, while the rates of cholesterol esterification and of mitochondrial cholesterol side-chain cleavage are unaffected. Conversely, ACTH inhibits cholesterol esterification. Therefore, γ3-MSH and ACTH together may coordinate a substantial shift in the set-point of cholesteryl ester ag cholesterol cycling toward the right. Because ACTH also activates cholesterol side-chain cleavage, this coordinate effect on the flux of cholesterol substrate is manifest as a potentiation of Corticosteroidogenesis by γ3-MSH. These data extend our previous studies demonstrating that pro-y-MSH polypeptides have an endocrine influence on the rat adrenal cortex.

The Inhibition of Rat Adrenal Cytochrome P-45011β Gene Expression by Androgens

The synthetic androgen methylandrostenediol (MAD) and the naturally occurring one, testosterone, both bring about hypertensive cardiovascular disease when chronically administered to rats. The pathogenesis of this form of experimental hypertension is thought to result from inhibition of steroid 11β-hydroxylase activity. In contrast to the above androgens, 19–nortestosterone, androstenedione and dehydroepiandrosterone (DHEA) have been reported to be without effect in elevating blood pressure. To examine the mechanism(s) involved, we have in this study compared the effects of a number of androgens on adrenal cytochrome P- 45011β enzyme and mRNA steady state levels. These parameters were also correlated with the ability of adrenal mitochondria isolated from these groups to hydroxylate 11–deoxycorticosterone (DOC) to corticosterone and 18–hydroxy-11–deoxycorticosterone (18–hydroxy-DOC). Rats treated for seven days with 10 mg per day of dihydrotestosterone, testosterone, 19–nortestosterone or MAD showed a prof...

Serum corticosteroids at the high and low points of the circadian rhythm in rats with regenerating adrenals

Abstract Serum levels of 11-deoxycorticosterone (DOC), 18-hydroxy-11-deoxycorticosterone (18-OH-DOC) and corticosterone (B) were determined at the high (1800 h) and low (0800 h) points of the circadian rhythm in control rats and in rats with regenerating adrenals. The levels of DOC at 0800 h in quiescent rats with regenerating adrenals were 6.5 times greater than in the control group. The levels of 18-OH-DOC and B, however, were not significantly different between these groups. A circadian rhythm for B, 18-OH-DOC and DOC was evident in control rats with a 12,20 and 3.5 fold increase, respectively, at 1800 h as compared to 0800 h. In animals with regenerating adrenals there was only a minimal change in the levels of B and 18-OH-DOC at 1800 h. There was, however, a 2 fold further increase in the levels of DOC at 1800 h as compared with the elevated levels at 0800 h. These findings show that the decrease in 11β and 18-hydroxylase activity of the regenerating adrenal is most clearly evident at the high point of the circadian rhythm. Furthermore, only by taking into account physiological variations in adrenal activity can an accurate assessment of DOC secretion in the adrenal regeneration model of hypertension be obtained.

Resistance of W/Fu rats to adrenal regeneration hypertension.

Summary The procedure for producing adrenal regeneration hypertension did not cause an increase in the systolic blood pressure of W/Fu animals. The regenerating adrenal gland in W/Fu animals was not restored to normal; reduced numbers of mitochondrial cristae were seen and the mitochondria were smaller in size; regeneration was complete in Sprague-Dawley rats of the Holtzman strain and there was a severe form of hypertensive, cardiovascular disease. The authors are grateful to Mrs. Yam Pun, Mrs. Neonile Fylypiw, Mr. Luther Joseph, Mrs. Geneva Joseph, Mrs. Elisabeth Lawson, and Mr. Robert Linsmair for skilled technical assistance.

Effect of testosterone on the rat adrenal cortical 11β-hydroxylation system☆

Abstract The influence of testosterone on the adrenal mitochondrial steroid hydroxylation system was investigated in the female Sprague-Dawley rat. After the injection of animals with testosterone for 10 days, it was possible to demonstrate impairment of progesterone metabolism in adrenal homogenates. The formation of corticosterone and 18-hydroxy-11-deoxycorticosterone was lower than in controls and there was an accumulation of 11-deoxycorticosterone (DOC). Adrenal mitochondria isolated from testosterone-treated rats showed low rates of conversion of DOC-4-14C to corticosterone and 18-hydroxy-DOC, confirming the low activity of steroid 11β- and 18-hydroxylases. Rates of corticosterone formation from unlabeled DOC were also lower in adrenal mitochondria from testosterone-treated animals. Accompanying these low steroid hydroxylation activities in isolated mitochondria were decreased levels of adrenal mitochondrial cytochrome P-450. In addition, spectral studies revealed that the DOC-induced spectral change was considerably less in the adrenal mitochondria from testosterone-treated rats. The results described in this communication are consistent with the concept that, after injection into the rat, testosterone reaches the adrenal cortex and there interacts with the mitochondrial cytochrome P-450 in such a way that the natural substrate, DOC, is less able to be bound and hydroxylated. This hypothesis was confirmed by the addition of testosterone to rat adrenal mitochondria in vitro and the observation of inhibition of both DOC-induced spectral changes and steroid hydroxylation.