Measurement of messenger ribonucleic acid for luteinizing hormone beta-subunit, alpha-subunit, growth hormone, and prolactin after hypothalamic pituitary disconnection in ovariectomized ewes.

A transnasal, transsphenoidal surgical approach was used to perform hypothalamic pituitary disconnections (HPD) in ovariectomized (OVX) ewes to examine the role of the hypothalamus in regulating the synthesis of anterior pituitary hormones. Ewes were killed at 1-3 days (n = 6), 1 week (n = 5), or 1 month (n = 5) after HPD. Pituitary glands were removed, and hemisected for analysis of hormone or messenger RNA (mRNA) content. Blot hybridization using specific complementary DNA probes was used to quantify the concentration of mRNA for LH beta-subunit, alpha-subunit, GH, and PRL. Concentrations of mRNA for LH beta- and alpha-subunits were lower (P less than 0.01) at 1-3 days after HPD than in OVX ewes. At 1 week and 1 month after HPD, concentrations of mRNA for LH beta- and alpha-subunits were near the lower limit of detection of this assay system. In contrast, for 30 days after HPD, pituitary concentrations of mRNA for GH and PRL were not different (P greater than 0.05) from those in OVX ewes. At 1 week and 1 month after HPD, pituitary content of LH, FSH, and GH was lower (P less than 0.01) than in OXV ewes. Pituitary PRL content in all HPD ewes was lower (P less than 0.05) than in OVX ewes. In a separate group of five ewes that were bled daily for 30 days after HPD, serum concentrations of LH and FSH fell dramatically during the first 3 days after HPD. In contrast, serum concentrations of GH and PRL remained similar to pre-HPD concentrations for 30 days after HPD. Thus, hypothalamic stimulation is essential for maintaining the concentration of mRNA for LH beta- and alpha-subunits within the anterior pituitary gland. Without continued hypothalamic support, pituitary and serum concentrations of LH and FSH rapidly decline. In contrast, concentrations of mRNA for GH and PRL are maintained in the absence of hypothalamic input.