Luteinizing Hormone Secretion from Anterior Pituitary Cells of the Cockerel: Evidence for an Ultradian Rhythm

Abstract

Studies were conducted to characterize the secretory pattern of luteinizing hormone (LH) from perifused anterior pituitary cells of the cockerel in the presence and absence of secretagogues. Basal LH secretion was found to occur in a rhythmic pattern, with the mean cycle period for 5 different perfusion columns estimated to be 66.4 ± 4.0 min. By contrast, when cells were repeatedly exposed to luteinizing hormone-releasing hormone (LHRH) at 90-min intervals, the period of the LH rhythm was altered to approximate the interval of LHRH pulses (96.7 ± 6.1 min; n = 3 perfusion columns). Exposure of cells to media containing 50 mM potassium chloride (KCl) augmented the release of LH and slightly decreased the cycle period compared to that which occurs during basal secretion (49.2 min) but did not eliminate the rhythm. Finally, perifusion of cells with medium containing 10 μM colchicine eliminated the rhythm of secretion.These data suggest that there exists an ultradian rhythm of LH secretion from the chicken pituitary which is expressed in the absence of hypothalamic input and is modified by the hypothalamic releasing factor, LHRH. In addition, the rhythm does not seem to be affected in the short-term by a small depolarization of the membrane as occurs with the addition of KCl to the perifusion media but does seem to be dependent upon microtubule function.