Subordinate female marmoset monkeys remain anovulatory and have low plasma concentrations of luteinizing hormone (LH) when maintained with their dominant females. Olfactory cues from the dominant female have been implicated in maintaining this reproductive suppression. Subordinate females that received either ablation of the vomeronasal organ (an accessory olfactory organ; n = 3), ablation of the main olfactory epithelium (n = 4), or both lesions (n = 5) did not ovulate in the following 7 weeks while housed with their dominant female. Plasma LH concentrations following either or both lesions were similar to pre-lesion concentrations. Olfactory lesions (verified by histological and behavioural trials) did not impair reproductive activity, as olfactory-lesioned dominant females underwent ovarian cycles of similar duration to intact dominant females. Lesioned subordinate females (n = 6), maintained in visual-only contact with their dominant female and group ovulated 29.1 ± 9.3 days (mean ± sem) after physical separation from their dominant females; this first onset of ovulation was significantly delayed (P < 0.05) compared with intact subordinate females completely isolated from their dominant females and group (10.8 ± 1.3 days, n = 8). Behavioural and visual cues together with olfaction all appear to play important roles in maintaining the suppression of ovulation in subordinate female marmoset monkeys.
J. Barrett, D. H. Abbott and L. M. George
J. Barrett, D. H. Abbott and L. M. George
Summary. Pheromonal signals from the dominant female marmoset monkey were implicated in maintaining the suppression of LH secretion and ovulation in socially subordinate females. When subordinate, and reproductively suppressed, female marmoset monkeys were removed from their group without scent contact with their dominant females, subordinate females in control group 1 (N = 8) and control group 2 (N = 5), ovulated 10·8 ± 1·4 days and 10·4 ± 0·8 days respectively (mean ± s.e.m.) after separation. Subordinate females (N = 8) removed from their dominant female and group, but maintained in scent contact only with their dominant females, showed a delay in the onset of ovulation (31·0 ± 6·4 days) compared with control groups 1 and 2. Plasma LH concentrations of subordinate females during the scent transfer phase were lower than in controls without scent transfer and comparable to those seen whilst the females were subordinates in groups. Contact of subordinate females with olfactory stimuli from dominant females therefore maintains the suppression of both LH secretion and ovulation in socially subordinate female marmosets. Such pheromonal cues provide evidence of a quantifiable link between dominant female marmosets and the maintenance of physiological suppression of reproduction in their female subordinates.
Keywords: marmoset; reproductive suppression; pheromones; ovulation; progesterone
C. R. Barb, J. B. Barrett, J. T. Wright, R. R. Kraeling and G. B. Rampacek
Summary. The effects of naloxone and β-endorphin on LH secretion by pig pituitary cells were studied in primary cultures. On Day 4 of culture, cells (105 seeded/well) were challenged with 10−9, 10−8 or 10−7 m gonadotrophin-releasing hormone (GnRH), 10−10, 10−9, 10−8 or 10−7 m-β-endorphin or 10−6 m-naloxone individually or in combinations. Secreted LH was measured at 4 h and 24 h after treatment and cellular content of LH was measured after 24 h. Basal LH secretion (control) was 23·5 ± 7·6 and 36·9 ± 10·3 ng/well at 4 h and 24 h, respectively. Relative to control at 4 h, 10−9, 10−8 or 10−7 m-GnRH stimulated (P < 0·05) LH secretion 140%, 210% and 250%, respectively. At 24 h, LH secretion was increased (P < 0·05) by GnRH compared to control, but the does–response to GnRH was absent. Naloxone increased (P < 0·01) LH secretion 166 ± 13% at 4 h and 141 ± 13% (P < 0·06) at 24 h. Secretion of LH after simultaneous addition of 10−8 m-GnRH plus naloxone was greater (P < 0·01) than after GnRH alone at 4 h but not at 24 h. β-Endorphin at 10−10, 10−9, 10−8 or 10−7 m failed to alter basal LH secretion at 4 h but decreased secretion at 24 h, while cellular LH content was similar to control at 24 h. LH secretion after simultaneous addition of 10−7 m-GnRH and 10−7 m-β-endorphin was less (P < 0·01) than after GnRH at 4 h but not at 24 h, while 10−10 m-β-endorphin plus 10−9 m-GnRH failed to suppress LH secretion, compared to GnRH alone. These results indicate that endogenous opioids may directly modulate LH secretion at the level of the pituitary.
Keywords: opioid; LH; pituitary; pig