Divergent reproductive endocrinology of the estrous cycle and pregnancy indwarf hamsters (Phodopus)

Progesterone (P4) and prolactin (PRL) in peripheral circulation of Siberian hamsters (Phodopus sungorus) throughout an estrous cycle and pregnancy wer e determined by repeated, small volume sampling from individuals housed in modified home cages. As predicted, the endocrinology of P. sungorus reprodu ction is similar to the rat, mouse and golden hamster and shows none of the eight distinctive features known for Djungarian hamsters (Phodopus campbel li). Specifically, in P. sungorus there is no evidence for resumption of pi tuitary PRL surges in late pregnancy, P4 concentrations during the differen tiation of the: corpus luteum on day 2 of pregnancy are higher las opposed to lower) than concentrations on the comparable day of an unmated estrous c ycle (diestrus 1), P4 concentrations increase throughout pregnancy. PRL sur ges are common during the estrous cycle, including a reliable surge on proe strus, and P4 plays an important role in facilitating the expression of beh avioral receptivity. We conclude that 'novel' P, campbelli reproductive end ocrinology has evolved since a common ancestor was shared with P. sungorus. With a time frame (the available time since the divergence of the two spec ies) and an ecological context (known niches and behavior in the wild) thes e: species offer the opportunity to study endocrinological evolution in pro gress. (C) 1999 Elsevier Science Inc. All rights reserved.