Physiological significance of altered insulin metabolism in the conscious rat during lactation.
Uptake of radioactively labelled insulin by the mammary gland of the rat increased 12-fold in lactation compared with non-lactating controls. This uptake was decreased by the presence of unlabelled insulin, indicating that it occurred via insulin receptors. The plasma half-life of insulin is decreased in lactation from 9.4 min to 4.8 min, and the metabolic clearance rate for insulin increased from 7.26 to 13.03 ml/kg body wt. per min. The basal insulin and glucose concentrations in the plasma were decreased in lactation. Infusion of insulin at a dose which led to a small physiological rise in plasma insulin concentration increased lipogenic rates in the mammary gland by 100% without causing marked hypoglycaemia. It is concluded that the lactating mammary gland is a highly insulin-sensitive tissue and that the lower plasma insulin during lactation occurs primarily as a result of this sensitivity increasing extraction of glucose by the gland and thus producing a decrease in the plasma glucose concentration. It is suggested that a secondary result of the fall in plasma insulin concentration is the preferential direction of substrates (glucose and non-esterified fatty acids) towards the lactating mammary gland and away from adipose tissue and the liver.
D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D005260:Female; D007328:Insulin / Q000097:blood / Q000378:metabolism*; D007774:Lactation; D008321:Mammary Glands, Animal / Q000378:metabolism*; D008657:Metabolic Clearance Rate; D011247:Pregnancy; D051381:Rats; D011919:Rats, Inbred Strains; D013004:Somatostatin / Q000494:pharmacology; D014018:Tissue Distribution
D001786:Blood Glucose; D007328:Insulin; D013004:Somatostatin