Luteinizing hormone in the bovine pars tuberalis: secretion in response to luteinizing hormone releasing hormone and intracellular isoforms.

The objective of this study was to examine the physiological characteristics of gonadotropes in the bovine (b) pars tuberalis as assessed by their ability to release Luteinizing Hormone (LH) in response to LH-Releasing Hormone (LHRH) and the intracellular distribution of LH isoforms. At slaughter, the stalk median eminence and associated pars tuberalis as well as the anterior pituitary gland were collected from each of 7 castrate males. Each stalk median eminence and pituitary gland was mid-sagitally sectioned and weighed. One half of each tissue was immediately frozen and subsequently homogenized to determine the intracellular distribution of bLH isoforms. Tissue extracts were desalted by flow dialysis against water and chromatofocused on pH 10.5-7.0 gradients. The remaining half of the pituitary was sliced with a Staddie-Riggs slicer. The pituitary slices and the remaining half of the stalk median eminence were perifused (0.1 ml/min) for a total of 360 min with effluent samples (1.0 ml) collected every 10 min. At 130 min tissues were stimulated with 5 x 10(-8) M LHRH. Concentrations of LH in the effluent samples and the fractions collected from chromatofocusing were determined by radioimmunoassay. The release of LH in response to LHRH was 43.9% and 47.0% above basal secretion for the pars tuberalis and pituitary, respectively, suggesting similar degrees of responsiveness. Pars tuberalis and pituitary extracts resolved into nine LH isoforms during chromatofocusing and were coded with letters beginning with the most basic form. No differences (P greater than .05) were observed in distribution of LH isoforms between the pars tuberalis and the pituitary gland.(ABSTRACT TRUNCATED AT 250 WORDS)