Inactivation of adrenocorticotropin, α- and Β-melanocyte-stimulating hormones, vasopressin, and pituitary fraction H by adipose tissue

Abstract

Rat adipose tissue homogenate contains a peptidase or group of peptidases which abolish the adipokinetic activity of ACTH, α-MSH, Β-MSH, vasopressin, and pituitary fraction H. The peptidase system is attached to an insoluble component in the homogenate. Homogenized rabbit adipose tissue inactivates only α-MSH, and homogenized guinea pig adipose tissue does not reduce the adipokinetic activity of any of the above hypophyseal peptides. Operation of the peptidase system in surviving slices of rat adipose tissue is suggested by these characteristics of this tissue: (a) rapid disappearance of adipokinetic activity from peptide-containing incubation medium; (b) absence of response to Β-MSH, vasopressin, or fraction H; (c) cessation of response to ACTH within 1 hr after exposure to the peptide is terminated. In contrast, slices of adipose tissue from the rabbit or guinea pig do not cause the disappearance of a detectable amount of activity from the medium; these slices are responsive to Β-MSH, vasopressin, and fraction H; their response to ACTH continues for at least 2 hr after exposure to the hormone is terminated. Differences between species in responsiveness of their adipose tissue to hypophyseal peptides appear to be related to differences in peptidase content of the fat cell.