Adipokinetic Actions of Adrenocorticotropin, Thyroid-Stimulating Hormone, Vasopressin, α- and β-Melanocyte-Stimulating Hormones, Fraction H, Epinephrine and Norepinephrine in the Rabbit, Guinea Pig, Hamster, Rat, Pig and Dog
Several naturally occurring polypeptide and amine hormones possess adipokinetic activity. The present investigation compares the adipokinetic activity of these hormones in the rabbit, guinea pig hamster, rat, pig and dog. Activity was assayed by measuring the effect of various concentrations of hormone upon the production of free fatty acids (FFA) by slices of perirenal adipose tissue incubated in Krebs-Ringer phosphate solution. As described by previous investigators, when the medium does not contain albumin, the FFA produced by lipolysis accumulate only within the tissue slice; when albumin is present in the medium, the FFA produced by lipolysis accumulate in the medium as well as in the tissue slice. In the albumin- free assay system, the concentration of FFA in the tissue after 3 hours' incubation is linearly related to the logarithm of the concentration of hormone in the medium. The following 6 components of the pituitary gland possess adipokinetic activity upon the adipose tissue of one or more mammalian species: ACTH, TSH, α-MSH, β-MSH, arginine vasopressin and fraction H. The slopes of the dose-response equations for the adipokinetic action of these 6 pituitary components do not show a statistically significant difference from each other. Epinephrine and norepinephrine also possess high adipokinetic activity in certain species. Each of these 8 hormones exhibits marked variation in the magnitude of its action upon the adipose tissue of different species. Each hormone possesses high activity in some mammalian species and no detectable activity in others. α-MSH and β-MSH possess an identical pattern of species variation. Another pattern is exhibited by epinephrine and norepinephrine. Additional different patterns of species variation are shown by each of the other adipokinetic hormones. Correlation of amino acid sequences of naturally occurring polypeptides with their adipokinetic activities suggests that an arginine moiety is essential for adipokinetic activity in this class of adipokinetic substance. Arginine vasopressin possesses adipokinetic activity while lysine vasopressin does not.