Plasma progesterone in snakes

Seasonal variation in plasma and corpus luteum oestradiol-17β and progesterone concentrations of the lizardCordylus p. polyzonus(Sauria: Cordylidae)

“…In the garter snake Thamnophis e/egans (Highfill & Mead 1975), plasma progesterone increased between the lirst and second trimester of gestation, but declined during the last trimester. Similar changes were recorded for the snakes Nerodia sipedon and Thamnophis e/egans (Chan, Ziegel & Callard 1973). In Cordylu.s p. polyzonus plasma progesterone concentrations progressively increased as pregnancy proceeded, reaching highest values two months prepartum and declined during the last month of pregnancy.…”

Hormonal Regulation of Ovarian Function in Reptiles

“…In-vitro studies demonstrate that corpora lutea of oviparous turtles (Klicka & Mahmoud, 1972) and viviparous lizards (Xavier, 1982;Girling & Jones, 2003) can convert pregnenolone to P 4 , and the rate of P 4 secretion by non-luteal ovarian tissues is insignificant compared with its rate of production by corpora lutea (Xavier, 1987;Bennett & Jones, 2002). However, at variance with this pattern, the viviparous skink Niveoscincus microlepidotus (Girling, Jones, & Swain, 2002) and viviparous snake Natrix sipedon pictiventris (Chan, Ziegel, & Callard, 1973) exhibit, in addition to peaks during gestation, significant preovulatory rises in plasma P 4 concentrations, which may reflect P 4 synthesis by the preovulatory follicles. The intensity of 3b-HSD activity in the corpus luteum has been positively correlated with plasma P 4 concentrations in both oviparous and viviparous species (Shanbhag, Radder, & Saidpur, 2001;Martínez-Torres, Hernández-Caballero, Alvarez-Rodriguez, Luis-Díaz, & Ortíz-López, 2003), although in some viviparous species the placentae may take over the primary role in P 4 production during later gestation (Guarino et al, 1998).…”

Changes in Plasma Progesterone in Relation to Vitellogenesis and Gestation in the Viviparous Snake Vipera aspis

“…The situation with physiological and (especially) endocrinological studies is, however, quite different. Despite an abundant literature (Highfill and Mead, 1975a,b;Callard et al, 1972;Yaron, 1972;Chan et al, 1973;Guillette et al, 1981;Mead et al, 1981;Kleis-San Francisco and Callard, 1986;Callard et al, 1992;Gobbetti et al, 1994), we still have no clear idea of how the evolution of viviparity has been achieved at a mechanistic level. For example, what hormones have been modified (either in levels of production or in their effects) and what tissues (both maternal and foetal) have been changed to allow long-term retention of the offspring in utero?…”

“…Although levels of this hormone are typically elevated during pregnancy in viviparous vertebrates, the role of this steroid is not always clear, even in intensively studied taxa, such as mammals (Cake et al, 1980;Thibault and Levasseur, 1991). In the case of reptiles, are progesterone levels higher in reproducing females than in nonreproducing females (Chan et al, 1973;Mead et al, 1981;Naulleau and Fleury, 1990;Saint Girons et al, 1993)? Are progesterone levels in the plasma as high in males as in females, as reported by Saint Girons et al (1993)?…”