Effect of β-Lipotropin on Aldosterone Production in the Isolated Rat Adrenal Cell Preparation*

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Abstract
Stimulation of aldosterone and corticosterone production by pituitary peptides structurally or biosynthetically related to ACTH was investigated in suspensions of isolated rat adrenal glomerulosa and fasciculata cells, respectively. Three different preparations of highly purified ovine or human .beta.-lipotropin (.beta.LPH) were tested. In contrast to synthetic ACTH-(1-24), which stimulated aldosterone secretion at concentrations of 10-12-10-11 M, .beta.LPH concentrations of 10-8-10-6 M were required for significant stimulation. Stimulation of corticosterone production by .beta.LPH preparations generally paralleled their aldosterone-stimulating activity, and most steroidogenic activity could be accounted for by immunoreactive ACTH, as determined in 2 ACTH radioimmunoassays. Synthetic human .beta.LPH-(37-58), which contains the 47-53 heptapeptide sequence common to .beta.LPH and ACTH, had aldosterone- and corticosterone-stimulating activities similar to those of equimolar concentrations of .beta.LPH, whereas synthetic fragments of the COOH-terminal (61-91) portion of .beta.LPH had no steroidogenic activity. Part of the slight steroidogenic activity of purified .beta.LPH preparations apparently is due to contaminating ACTH, and part is due to the intrinsic ACTH-like activity conferred upon .beta.LPH by the amino acid sequence shared with ACTH. In contrast to ACTH, the concentrations of .beta.LPH required to stimulate adrenal steroidogenesis were 102-105 times greater than normal plasma levels, indicating that physiological pituitary .beta.LPH secretion has no direct role in regulating the secretion of aldosterone.