The elevation of endogenous prolactin secretion using thyrotopin releasing hormone was associated with significant increases in mammary milk production in postpartum women. More-over, a specific effect was seen on the percent fat composition which has been shown to rise as much as 228% over pretest conditions. As in the bovine, administration of high doses of estrogen is associated with mammary breast development and the sudden removal of this stimulus if accompanied by nipple stimulation is associated with non-puerperal lactation. The inhibitory effects of estrogen on the mammary cellular response to circulating prolactin has been deduced from studies in pregnant and parturient women by measuing the TRH-induced prolactin response. These studies support a relationship between prolactin and sex steroids on the initiation and maintenance of human lactation.
PIP: The relationship between the secretion of pituitary prolactin (hPRL) and the initiation and maintenance of human lactation was investigated. HPRL secretion was stimulated by suckling and the change was especially significant beyond the 8th postpartum day when basal hPRL concentrations return to prepregnancy levels. Intravenous thyrotropin releasing hormone (TRH) further elevated hPRL and was associated with significant increases in mammary milk production in postpartum women. Milk fat concentrations were also seen to rise, as much as 228% over pretest conditions. TRH but not suckling increased plasma pituitary thyrotropin (hTSH) concentrations. Administration of estrogens led to decreased secretion of LH and FSH, indicating a potentiating effect on the hypothalamus and/or pituitary gland. Estrogens also were associated with mammary breast development; removal of this stimulus if accompanied by nipple stimulation led to nonpuerperal lactation.