Effect of pinealectomy on plasma melatonin, prolactin and progesterone concentrations during seasonal reproductive quiescence in the tammar, Macropus eugenii.

Non-lactating female tammars were pinealectomized (N = 5) or sham-operated (N = 6) in October, during the austral period of increasing daylength. After autopsy in February the completeness of pinealectomy was assessed by histological examination of the epithalamic region. Pinealectomy, but not the sham-operation, abolished the nocturnal rise in plasma melatonin but weekly plasma prolactin concentrations were similar in both groups from October to February. Plasma progesterone concentrations remained low (less than 160 pg/ml) in both groups until after the summer solstice in December, when there was a 2-4-fold increase (greater than 300 pg/ml) by late January, indicating reactivation of the quiescent corpus luteum. The mean date of birth or oestrus for the pinealectomized tammars was January 11 +/- 4.8 days (s.e.m.), and for the sham-operated tammars January 24 +/- 5.1 days. These results demonstrate that the pineal is not necessary for the maintenance of seasonal quiescence or to induce reactivation of the corpus luteum at the start of the normal breeding season after the summer solstice.