Melanocyte-stimulating activity in fetal, newborn and adult guinea-pigs: studies of the pituitary, blood plasma and amniotic fluid.
Melanocyte-stimulating activity in the pituitary and plasma of fetal, newborn and adult guinea-pigs, and in amniotic fluid, was bioassayed on isolated Anolis skin. In the fetuses, levels in the posterior, anterior and whole pituitary increased exponentially between 39 and 70 days of gestation; in all cases, the increases were close to 35-fold in terms of ng/lobe, and 6-fold in ng/mg of lyophilized tissue. The increases were due to growth, and to an increased accumulation within the tissues. Ratios of activity in the posterior pituitary: anterior pituitary: hypothalamus approximated 200:30:1 (ng/mg of dry tissue). Fetal plasma levels showed some scatter; however, there were no trends with age, and the average value (10.0 +/- 1.6 ng/ml) was close to that of the mothers (10.6 +/- 2.6 ng/ml). Plasma activity appeared to fall markedly around birth; newborn pups, 2-6 hours after birth, showed levels 65% below those of the fetuses, and also below those of the adults (significant; P less than 0.05). At the same time the pituitary levels increased; this suggested a shut-down in release. The possible implications of this in the birth processes are discussed. Amniotic fluid showed only low, inconsistent activity, below 1% of plasma levels.
D000653:Amniotic Fluid / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001790:Blood Physiological Phenomena; D005260:Female; D005333:Fetus / Q000502:physiology*; D006168:Guinea Pigs; D009074:Melanocyte-Stimulating Hormones / Q000502:physiology*; D010902:Pituitary Gland / Q000502:physiology*; D011247:Pregnancy
D009074:Melanocyte-Stimulating Hormones