Association of prolactin and insulin receptors with mammogenesis and lobulo-alveolar formation in pregnant ewes

Abstract

1. 1. Pregnant, multiparous ewes were sacrificed at d50 ( n = 3), 80 ( n = 4), 115 ( n = 3), or 140 ( n = 4) for biochemical, histological and autoradiographical quantitation of mammary growth. 2. 2. Significant increases in concentration of mammary parenchyma DNA (0.25–24 mg/g tissue), total udder DNA (57–1304 mg), and total udder RNA (36–1504 mg) were observed by d 115. 3. 3. Mammary tissue at d 115 contained the maximal percent of tissue volume occupied by epithelium (41.2%), number of cells per alveolar cross section (36.6) and percent of [methyl- 3 H]-thymidine labeled epithelial cell nuclei (3.5%). 4. 4. Concentration prolactin binding sites were significantly increased at d 115 of gestation, but serum prolactin and growth hormone concentrations remained low until d 140. 5. 5. Mammary insulin binding sites (per unit membrane protein) progressively decreased during gestation. 6. 6. Results suggest that serum growth hormone concentration and quantity of insulin receptors do not limit mammogenesis but greater concentrations of prolactin binding sites coincident with lobulo-alveolar formation, suggest a primary association with mammogenesis in the ewe.