A cytochemical study of the adrenal cortex regenerating after enucleation

Adrenal morphometry in unilateral and sham adrenalectomized Syracuse high and low avoidance rats

Syracuse high (SHA) and low (SLA) Long-Evans rats, bred for differences in avoidance performance, exhibit dramatic differences in adrenal gland weight. Here we examined adrenal weight and composition (i.e., the size of the medulla, zonae fasciculata/reticularis and glomerulosa) following unilateral adrenalectomy and sham surgery in these strains. Adrenals of SLA animals, regardless of treatment, were heavier and contained larger medullas and cortices than did adrenals of SHA animals. When individual regions were expressed as a percent of total adrenal area, SHA glands (age 31-45 days), although smaller in weight, contained a larger percentage of glomerulosa than did adrenals of SLA animals. Unilateral adrenalectomy produced significant compensatory growth in SHA and SLA animals as indexed by increases in adrenal weight as soon as 7 days after surgery. The adrenal enlargement was the net result of an increase in absolute size of the fasciculata/reticularis (significant 14 days following surgery) and a decrease in the absolute size of glomerulosa (significant 7 days following surgery). These results suggest that SHA and SLA adrenal differences may be the result of genetically determined differential pituitary-adrenal activity.

Failure of melatonin to inhibit the mitotic activity of regenerating adrenal cortex in rats

Although there is little evidence that melatonin may have a direct antimitotic effect on various cells, it has been shown that this pineal compound may influence the cell proliferation of either normal or neoplastic cells. Therefore, the influence of melatonin on the mitotic activity of regenerating adrenal cortex of rats was studied. The mitotic activity was counted in the adrenal cortex or rats on days 2, 7, and 12 following enucleation of the adrenals. Melatonin did not influence the mitotic activity of regenerating adrenal cortex in the rat.

Control of adrenocortical growth in vivo

Adrenocortical growth is discussed with respect to its relation to body weight, elevated ACTH (provoked by sustained stress, adrenal enzyme deficiency, and adrenal enucleation), and unilateral adrenalectomy. It seems likely that these three conditions under which adrenal growth occurs are each controlled and mediated by different agents. Least is known about the growth of adrenals with the growth of the organism; however, because treatment with growth hormone is known to stimulate adrenal mitogenesis, and because adrenals grow in proportion to body growth by increasing cell number, it is proposed that this growth may be mediated by growth hormone (via somatomedin). ACTH causes primarily adrenocortical cellular hypertrophy which is subsequently followed by hyperplasia. It has been shown that the application of a sustained stressor, induction of adrenal enzyme deficiency and adrenal enucleation all result in persistent elevation in circulating ACTH levels and adrenal growth. It appears that the stimulus to ACTH secretion is a virtual or real decrease in corticosteroid feedback signal, and that ACTH secretion is regulated by corticosteroid levels. An additional humoral factor may be triggered by adrenal enucleation, and the possibility that a fragment of the N-terminal peptide of the ACTH precursor molecule plays this role is entertained. Finally, the evidence that the proliferative adrenal growth after unilateral adrenalectomy is mediated by afferent and crossed efferent neural pathways, and is regulated by aldosterone, pineal peptides and exposure to constant light is discussed.

An electron microscopic study of the regenerating adrenal gland during the development of adrenal regeneration hypertension

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