Comparison of Intracellular and Secreted Isoforms of Bovine and Ovine Luteinizing Hormone1

The media (secreted isoforms) and tissue extracts (intracellular isoforms) from ovine and bovine pituitaries perifused in vitro were chromatofocused to examine the pattern of LH isoforms secreted. At slaughter, anterior pituitaries from castrated male cattle (n = 6) and sheep (n = 4) were collected, sectioned mid-sagitally, and weighed. One half was immediately frozen and used to assess intracellular isoforms of LH. The remaining half was sliced and perifused for 120 min to allow attainment of a stable basal secretion rate and then stimulated with 5 x 10(-8) M LHRH. Effluent samples were collected and assayed for LH. Samples representing basal or LHRH-induced secretion were pooled, dialyzed against water, and lyophilized. Pituitary extracts were desalted by flow dialysis against water. All samples were chromatofocused on pH 10.5-7.0 gradients, and concentrations of LH in eluant fractions were determined by RIA. LH in pituitary extracts resolved into nine peaks, which were coded with letters beginning with the most basic isoform. Isoforms A, B, and C were nondetectable (bovine; p less than 0.01) or constituted a smaller percentage of total LH (ovine; p less than 0.05) in perifusates compared to intracellular samples. The percentages of isoforms D and E were lower (p less than 0.05) in perifusates than in intracellular samples from the ovine extracts but similar for the bovine (p greater than 0.05). Isoforms F and G were proportionately higher (p less than 0.05) in basal (bovine) and LHRH-induced (bovine and ovine) samples than in intracellular samples.(ABSTRACT TRUNCATED AT 250 WORDS)