Effect of changing photoperiod on peripheral plasma prolactin and progesterone concentrations in the tammar wallaby (Macropus eugenii)

Abstract

Summary. In tammar wallabies kept in normal daylengths between the equinoxes, births occurred at the normal time after the summer solstice and the progesterone profile reflected this cycle. There were no significant changes in plasma prolactin. In tammars placed in a 15L : 9D photoperiod and then, 5 weeks later, in 12L :12D, births occurred 29\p=n-\36 days after the daylength was reduced. A characteristic transient peak of plasma progesterone occurred 8\p=n-\14 days after the change, indicating a delay of 3\p=n-\9 days in the resumption of luteal activity. Plasma prolactin levels were significantly higher (> 40 ng/ml) (P < 0\m=.\01)during the solstitial daylength, declining to <30 ng/ml within 14 days of the reduction in photoperiod. Animals kept in 12L : 12D and then in 9L :15D gave birth asynchronously after entry into the pens, suggesting that this daylength (12L:12D) is permissive. Changes in plasma progesterone reflected the resumption of luteal activity but no significant changes in plasma prolactin were observed.This study shows that the inhibition of the corpus luteum in seasonal quiescence can be maintained in the presence or absence of elevated prolactin levels, indicating that other factors, perhaps of pineal origin, may also be involved.

Evidence that the seasonally breeding Bennett's wallaby (Macropus rufogriseus rufogriseus) does not exhibit short-day photorefractoriness

“…The . However, in mid-to late seasonal quiescence, treatment with exogenous melato¬ nin or artificial short photoperiods are effective in terminating quiescence in both the tammar and Bennett's wallaby (tammar: Hinds & den Ottolander, 1983;McConnell & Tyndale-Biscoe, 1985; Bennett's wallaby: Loudon et al, 1985;. The increase in photoperiod after the winter solstice may therefore have the primary effect of initiating seasonal quiescence (via a pineal-dependent process) but a long period of exposure to increasing photoperiods may be required before short photoperiods or exogenous melatonin are capable of terminating seasonal quiescence.…”

“…'Present address: Department of Physiology and Pharmacology, University of Queensland, St Lucia, Queensland 4067, Australia. In seasonally breeding wallabies, reproduction is known to be under the control of photoperiod (reviewed by Tyndale-Biscoe et al, 1986). As in eutherians, seasonality in wallabies is controlled via a pineal-dependent mechanism involving the pattern of secretion of pineal melatonin (tammar wallaby: McConnell & Tyndale-Biscoe, 1985;McConnell & Hinds, 1985;McConnell et al, 1986; Bennett's wallaby: Loudon et al, 1985;Curlewis & Loudon, 1988a Flint & Renfree, 1982;Hinds & den Ottolander, 1983;Bennett's: Merchant & Calaby, 1981;Curlewis et al, 1986). There is a post-partum oestrus at which the majority of females mate and conceive.…”

Melatonin regulates delayed embryonic development in the short-nosed fruit bat, Cynopterus sphinx

“…Melatonin treatment was highly effective in lengthening the duration of the preimplantation period in mink and spotted skunk (Duby et al 1972, May & Mead 1986), while melatonin administration in marsupials terminates diapauses (Hinds & den Ottolander 1983, McConnell & TyndaleBiscoe 1985. In mink and spotted skunk, melatonin blocks implantation by suppressing prolactin (PRL) release (Berria et al 1989, Kaplan et al 1991.…”

“…Two species of marsupials, the tammar wallaby (Macropus eugenii) and Bennett's Wallaby (Macropus rufogriseus rufogriseus), exhibit embryonic diapauses after the winter solstice, when the corpus luteum and embryo remain in quiescence inspite of the presence of a pouch young (Curlewis et al 1987). Contrary to the mink and spotted skunk, treatment with exogenous melatonin during seasonal quiescence results in termination of diapauses in both the wallaby (Hinds & den Ottolander 1983, McConnell & Tyndale-Biscoe 1985. Bilateral removal of the superior cervical ganglion in female tammars eliminates seasonal embryonic diapause (Renfree et al 1981).…”

Melatonin implants prevent the onset of seasonal quiescence and suppress the release of prolactin in response to a dopamine antagonist in the Bennett's wallaby (Macropus rufogriseus rufogriseus)

“…From shortly after the winter solstice removal or loss ofthe pouch young does not cause reactivation of the CL in either species and the female remains in a state of reproductive quiescence which is known to be regulated by photoperiod (seasonal quiescence). In both the tammar and Bennett's wallaby artificial reductions in photoperiod or treatment with melatonin during the period of seasonal quiescence are capable of causing the reactivation of the quiescent CL (tammar: Hinds & den Ottolander, 1983;McConnell & Tyndale-Biscoe, 1985;McConnell et ai, 1986; Bennett's wallaby: Loudon et ai, 1985;Brinklow & Loudon, 1989).…”