STIMULATION OF INTRA-UTERINE GROWTH IN RAT BY α-MELANOCYTE-STIMULATING HORMONE

Abstract

SUMMARY We have studied whether endogenous α-MSH has a function in stimulating intra-uterine growth in the rat. The approach used was to determine whether or not this hormone is present during the intra-uterine growth spurt, and if binding of endogenous foetal α-MSH by antibodies would inhibit this growth. Antibodies against α-MSH or ACTH 1-24, either purified or non-purified, induced immunofluorescence in the intermediate lobe of adult male control rats. Using purified anti-α-MSH, fluorescence appeared in the foetal intermediate lobe on day 18 of pregnancy, the day that biologically active MSH was first seen. A negative correlation was observed between the pituitary MSH content and foetal body weight only on day 19 of pregnancy. Injection of purified anti-α-MSH induced a drop in foetal body weight, but no effect on placental weight was observed. Purified anti-ACTH 1-24 had no effect upon body weight but caused an increase in placental weight. These results support our previous findings and indicate that endogenous MSH has a function in the stimulation of foetal growth.