Effects of antibodies to bovine thyroid plasma membranes on in vitro basal and thyroid-stimulating hormone stimulation of bovine thyroid adenylate cyclase

Thyrotrophin blocking antibodies in the sera of mothers with congenitally hypothyroid infants

We examined IgG from 15 mothers of infants with congenital hypothyroidism for their ability to block TSH-stimulated iodine organification in vitro. Only one out of 15 of these IgGs exhibited TSH-blocking activity. This IgG could inhibit TSH action by 30-50%. It could not block radiolabelled TSH from binding to its receptor but did inhibit dibutyryl cyclic AMP stimulation of iodine organification implying a unique effect on post-receptor processes via a membrane binding site distant from the TSH binding site. Interestingly there was no evidence of autoimmune thyroid disease in the mother. These results suggest that the transplacental passage of TSH-blocking antibodies plays little, if any, role in the development of congenital hypothyroidism.

Prolactin-like activity of anti-prolactin receptor antibodies on casein and DNA synthesis in the mammary gland

Prolactin receptors were partially purified from rabbit mammary gland membranes by using an affinity chromatography technique. Antibodies against this prolactin receptor preparation were obtained in guinea pig and sheep. Both antisera were able to inhibit the binding of 125I-labeled ovine prolactin to rabbit mammary gland membranes. When added to culture media of rabbit mammary explants, the anti-prolactin receptor antiserum inhibited the capacity of prolactin to initiate casein synthesis and casein mRNA accumulation as a function of the antiserum concentration. However, in the absence of prolactin, both antisera (guinea pig and sheep) at moderate concentrations were capable of mimicking prolactin action on casein gene expression and on DNA synthesis. At higher concentrations, the anti-prolactin receptor antibodies inhibited their own actions. Several characteristics of the prolactin effect were also observed with the anti-prolactin receptor antibody: the stimulatory effect of the antibody was amplified by glucocorticoids; colchicine, which was capable of blocking prolactin action, also prevented the induction by the antibody. Lysosomotropic agents, which do not interfere with prolactin action, did not alter the response observed with the antibody. These results indicate that an anti-prolactin receptor antibody can mimic two major actions of prolactin obtained in mammary explant culture and suggests that the prolactin molecule is not required beyond the initial binding to its receptor.