Uptake of 125i-Labelled Human Placental Lactogen and Human Placental Lactogen by the Tissues of Normal and Lactating Rats

Prolactin receptors were identified and partially characterized in the mammary gland of the rat. The binding of 125I-labelled ovine prolactin to a subcellular particulate fraction of rat mammary gland decreased between days 30 and 100 of age. Over the same period, binding to the liver increased and there was a significant negative correlation between prolactin binding in the two tissues. Binding to the mammary gland was low during pregnancy, increased in early lactation and declined after the litters were weaned. Binding to the liver was lower during lactation than during pregnancy or the period after weaning suggesting that tissue-specific factors may operate in the control of this receptor. In virgin rats, prolactin binding by the mammary gland was increased by oestrogen. This effect was blocked by hypophysectomy and partially restored by replacement therapy with prolactin. Hypothyroidism and treatment with progesterone also reduced the response to oestrogen. The maintenance of prolactin binding by the mammary gland of lactating rats depends on the presence of the ovaries and pituitary, thyroid and adrenal glands. Examination of the ratio epithelium: stroma suggests that prolactin acts by increasing the number of epithelial cells in the mammary gland and that thyroid, adrenal and ovarian hormones modulate the number of receptors per cell.

Section: Discussionsupporting

confidence: 92%

Ontogeny and Control of Prolactin Receptors in the Mammary Gland and Liver of Virgin, Pregnant and Lactating Rats

Hayden¹,

Bonney²,

Forsyth³

1979

“…The presence of specific binding sites for prolactin does not of course prove that the hormone has physiological effects on electrolyte or water metabolism. Prolactin uptake may merely indicate that the kidney is an important organ for the clearance of lactogenic hormones from the drculation as shown for placental lactogen (Reddy & Watkins, 1975).…”

Section: Discussionmentioning

confidence: 99%

Prolactin Receptors in the Rat Kidney

Mountjoy¹,

Cowden²,

Dobbie³

et al. 1980

Specific binding of 125I-labelled ovine prolactin iodinated by a lactoperoxidase method was demonstrated in crude membrane preparations of kidneys and adrenals of male Sprague-Dawley rats and livers from female rats. Membrane preparations derived from the 100,000 g fractions of tissue homogenates contained most of the specific prolactin binding. Kinetic and affinity characteristics of prolactin binding to kidney membranes were examined in detail. Maximal specific binding occurred after incubation for 30 h at room temperature. Scatchard analysis indicated that prolactin binding to kidney membranes was of high affinity (dissociation constant = 1.4 x 10(-10) mol/l) and similar to that for liver membranes, although kidney membranes from male rats bound approximately sixfold less prolactin/mg membrane protein than did liver membranes from female rats. Specific prolactin binding was demonstrated in both renal medulla and cortex. Autoradiography showed maximal prolactin binding activity in the epithelial cells of the proximal tubule and faint activity in the tubular cells throughout the nephron. Specificity of uptake by proximal tubular cells was indicated by the gross reduction in prolactin activity when excess ovine prolactin was administered simultaneously. The demonstration of specific binding sites for prolactin localized primarily in the proximal tubules was consistent with renal action of prolactin, predominantly on sodium metabolism.

“…In a number of other autoradiographic studies on the binding of prolactin, 125I-labelled prolactin was administered in vivo and the differential localization of radioactive iodine was measured at various times after the injection of prolactin (Birkinshaw & Falconer, 1972;Rajaniemi et al 1974;Reddy & Watkins, 1975). Prolactin binding to tissue under these circumstances is a function of the half-life of the prolactin in the circulation ; it also assumes that the bound radioactive iodine is associated with undamaged hormone and that the injected hormone is capable of binding to receptors.…”

Section: Discussionmentioning

confidence: 99%

Autoradiographic Localization of the Binding of 125i-Labelled Prolactin to Rat Tissues in Vitro

Costlow¹,

McGuire²

1977

The binding of 125I-labelled prolactin to normal rat tissues was examined with autoradiographic techniques. Tissue slices were incubated with 125I-labelled ovine prolactin in the presence or absence of excess unlabelled hormone to distinguish between the specific and the non-specific localization of grains. Specific binding was found in the liver, adrenal gland and kidney from female rats, and in the mammary gland, ovary, testis and prostate gland. Conversely, fat, muscle, heart, lung, and spleen from female rats and uterine tissue did not bind 125I-labelled prolactin appreciably, or show competition for binding in the presence of unlabelled hormone. In the testis, prolactin bound exclusively to Leydig cells; in the prostate gland, binding was localized in the secretory epithelium. Kidney tubules in the cortex displayed specific prolactin localization whereas the medulla did not bind prolactin. Adrenal medulla showed no hormone binding; however, the zona reticularis and to a lesser extent the zona fasciculata bound prolactin. In the ovary, grains were limited to the theca and to a lesser extent the corpus luteum and follicles. In all cases, binding was essentially abolished when unlabelled prolactin was included in the incubation medium. These results confirm reports of the presence of prolactin receptors in these tissues and serve to identify the cells within a particular organ that respond to prolactin.