Suitability of the mammalian model in comparative reproductive endocrinology

Perhaps one should be impressed by the basic generality of many of the features of the mammalian HHG system. The applicability of this model to other groups argues for the generally conservative nature of the basic organization of the reproductive endocrine system. Even in cases where exceptions are apparent, we must be cognizant of the relatively narrow base of mammalian species on which the classical mammalian model is built. While reference to the mammalian system provides a useful first approach to studies on new groups, in view of the many exceptions in details of this system, it is important that we avoid undue constraints that might be imposed by the the mammalian model. In this connection it would seem advisable to test each principle carefully before assuming that it exists or is as important as in mammals. A particularly significant issue in this regard is the question of temporal organization of endocrine secretions: Both the existence and relative importance of discontinuous, pulsatile, stimulation must be explored in more groups. It must be emphasized that past experience has already shown us that a simple phylogenetic approach is not likely to provide a clear pattern for the similarities and differences in the reproductive endocrine system. Thus, we should not be too hasty in our extrapolations of data, even among closely related species.