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Two analogs of the hypothalamic luteinizing hormone releasing factor modified at the histidine-2 position were tested for biological activity (secretion of luteinizing hormone) in cultures of dispersed rat anterior pituitary cells. The analog in which glycine was substituted for histidine at position 2, [Gly(2)]LRF, behaves as a partial agonist releasing less than 50 percent of the luteinizing hormone secreted at maximum concentrations of the releasing factor, while the analog in which histidine at position 2 is deleted has no significant agonist activity at any of the doses tested. When added to the cultured cells at molar ratios 10(3) to 10(4) times that of the luteinizing hormone releasing factor, both analogs decrease the amount of luteinizing hormone secreted in response to the releasing factor.

The primary structure of ovine hypothalamic hypophysiotropic luteinizing hormone-releasing factor, LRF, has been established as pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH(2) by hydrolysis of the peptide with chymotrypsin or pyrrolidone-carboxylylpeptidase and by analysis of the products by an Edman-dansylation sequencing technique, as well as by mass spectrometry of the derived phenylthiohydantoins. A decapeptide with the proposed primary structure, prepared by total synthesis, gave the same result on sequencing. The synthetic decapeptide possesses the same biological activities as the native ovine LRF. The amino-acid sequence of ovine LRF is identical to that already published for porcine LRF.

Optically black, thin lipid membranes prepared from sheep erythrocyte lipids have a high dc resistance (R(m) congruent with 10(8) ohm-cm(2)) when the bathing solutions contain NaCl or KCl. The ionic transference numbers (T(i)) indicate that these membranes are cation-selective (T(Na) congruent with 0.85; T(Cl) congruent with 0.15). These electrical properties are independent of the cholesterol content of the lipid solutions from which the membranes are formed. Nystatin, and probably amphotericin B, are cyclic polyene antibiotics containing approximately 36 ring atoms and a free amino and carboxyl group. When the lipid solutions used to form membranes contained equimolar amounts of cholesterol and phospholipid, these antibiotics reduced R(m) to approximately 10(2) ohm-cm(2); concomitantly, T(Cl) became congruent with0.92. The slope of the line relating log R(m) and log antibiotic concentration was congruent with4.5. Neither nystatin (2 x 10(-5)M) nor amphotericin B (2 x 10(-7)M) had any effect on membrane stability. The antibiotics had no effect on R(m) or membrane permselectivity when the lipids used to form membranes were cholesterol-depleted. Filipin (10(-5)M), an uncharged polyene with 28 ring atoms, produced striking membrane instability, but did not affect R(m) or membrane ionic selectivity. These data suggest that amphotericin B or nystatin may interact with membrane-bound sterols to produce multimolecular complexes which greatly enhance the permeability of such membranes for anions (Cl(-), acetate), and, to a lesser degree, cations (Na(+), K(+), Li(+)).