TIMED DAILY ADMINISTRATIONS OF HORMONES AND ANTAGONISTS OF NEUROENDOCRINE RECEPTORS ALTER DAY-NIGHT RHYTHMS OF ALLOGRAFT-REJECTION IN THE GULF KILLFISH, FUNDULUS-GRANDIS

Immune activity during scale allograft rejection, measured by melanoph ore destruction, is two to three times greater at night (12-hr scotoph ases) than during the day (12-hr photophases) in gulf killifish (Fundu lus grandis). In the present study of killifish, hormones and antagoni sts of neuroendocrine receptors were administered daily at 0800 or 200 0 hr during either 12-hr photoperiods (light onset: 0800 hr) or contin uous light to examine possible neuroendocrine regulation of the allogr aft rejection rhythm. Immune activity peaked 0-12 hr after the time of daily growth hormone injections (0800 or 2000 hr) in fish held under continuous light and examined twice daily (0800 and 2000 hr) for melan ophore breakdown. Immune activity peaked 12-24 hr after the time of da y when cortisol-supplemented meals were provided (light onset or light offset) whether fish were treated throughout the days of melanophore examinations or pretreated for 3 days only prior to melanophore examin ations. Daily rhythms of immune activity were not observed in fish tre ated with propranolol or naloxone at light offset only, growth hormone or atropine at light onset only, or prolactin at either light onset o r light offset; these timed-treatments also reduced (prolactin or grow th hormone) or prolonged (propranolol or naloxone) the length of time needed to destroy all melanophores within an allograft compared with c ontrols. These results demonstrate that neuroendocrine factors can mod ulate a daily rhythm of immune function in fish. (C) 1995 Academic Pre ss, Inc.