Progesterone-binding plasma proteins (PBPP, progesterone-binding globulin, PBG, and corticosteroid binding globulin, CBG) have been measured in plasma of guinea-pigs, casiragua, cuis, degu and plains viscacha. During pregnancy PBPP increased to reach peak values between Days 20-25 and Days 50-term in guinea-pigs, immediately before parturition in casiragua, and in mid-gestation in cuis, degu and viscacha. The pattern of PBPP concentration during pregnancy was similar to that of plasma progesterone concentration, and the ratio of molar concentration of PBPP and progesterone was greater than 1 in all species. Plasma proteins were separated by chromatography on SP-Sephadex C-50, and from its chromatographic behaviour and progesterone-binding property evidence was obtained for an anionic, high-affinity PBG in the plasma of all the animals studied during gestation: Electrophoretic mobility of SP-Sephadex-purified PBG applied to 7% polyacrylamide gels differed between species, being highest for casiragua PBG and lowest for guinea-pig PBG. Binding capacities ranged from 0.5 to 4.8 X 10(-6) M, and association constants from 7.6 to 17.4 X 10(8) M-1. Ligand specificities differed between species and marked contrasts were found for certain steroid isomers. The average molecular weights measured by gel electrophoresis of PBG under denaturing conditions were similar in cuis, degu and viscacha and close to PBG I of guinea-pigs, while coypu PBG had a molecular weight of about one half, approximately 75000. It is concluded that PBG has been adopted in pregnancy as a progesterone-conserving mechanism in this suborder of rodents with long gestation periods relative to maternal body weight. Restricted homologies in the physico-chemical characteristics of PBG from various hystricomorph rodents suggest that interspecific differences in structure are considerable.

Abstract. Teleost retinal cones elongate in the darkand contract in the light. In isolated retinas of the green sunfish Lepomis cyanellus, cone myoids undergo microtubule-dependent elongation from 5 to 45 #m. We have previously shown that cone contraction can be reactivated in motile models of cones lysed with Brij-58. Reactivated contraction is both actin and ATP dependent, activated by calcium, and inhibited by cAMP. We report here that we have obtained reactivated cone elongation in lysed models prepared by the same procedures. Reactivated elongation is ATP dependent, activated by cAMP, and inhibited by calcium. The rate of reactivated elongation is proportional to the cAMP concentration between 10 #M and 0.5 mM, but is constant between 10 #M and 1.0 mM Mg-ATP. No elongation occurs if cAMP or Mg-ATP concentration is <5 ~M. Mg-ATP is required for both cAMP-dependent and cAMP-independent processes, suggesting that Mg-ATP is required both for a regulatory process entailing cAMP-dependent phosphorylation and for a force-producing process. Free calcium concentrations _> 10 -7 reduce the elongation rate by 78% or more, completely inhibiting elongation at 10 -5 M. This inhibition is not due to competition from calcium-activated contraction. Cytochalasin D blocks reactivated contraction, but does not abolish calcium inhibition of reactivated elongation. Thus calcium directly affects the elongation mechanism. Calcium inhibition is calmodulin dependent. The calmodulin inhibitor trifluoperazine abolishes calcium inhibition of elongation. Furthermore, calcium blocks elongation only if present during the lysis step; subsequent calcium addition has no effect. However, if calcium plus exogenous calmodulin are subsequently added, elongation is again inhibited. Thus calcium inhibition appears to require a soluble calmodulin which is lost shortly after lysis.

The effect of the presence of a preimplantation embryo on protein concentration, rate of protein synthesis, beta-glucuronidase and acid phosphatase activities, steroid metabolism and prostaglandin F production in caruncular and intercaruncular tissue have been studied for sheep at Day 15 of pregnancy. The rate of protein synthesis in both tissues was greater in pregnant than in non-pregnant animals, although the difference was only significant in caruncular endometrium. The effect in caruncular tissue was mimicked in ovariectomized animals treated with oestradiol. Localized changes in the caruncular tissue were observed in respect of PGF with an increased tissue concentration, an enhanced basal release when the tissue was incubated in the presence of indomethacin, and a decreased net production. Maximum production of PGF in the 2 tissues was unaffected by the presence of an embryo but it was enhanced by oestradiol or progesterone treatment in intercaruncular tissue of ovariectomized ewes. beta-Glucuronidase and acid phosphatase activities and steroid metabolism were unaffected by pregnancy. However, in ovariectomized animals oestradiol treatment stimulated beta-glucuronidase activity in endometrium and myometrium. Progesterone treatment stimulated acid phosphatase activity in the intercaruncular endometrium. The results show that amongst several endometrial constituents investigated relatively few changes were detected by Day 15 post coitum, one day before definitive attachment. Those changes that did occur were associated with the dynamics of PGF production and the rate of protein synthesis, and were consistent with the production of a PGF binding component in caruncular endometrium which may be concerned with the protection of luteal function by redirection of uterine PGF production. Canonical variate analysis revealed that changes on Day 15 of pregnancy were mimicked most closely in caruncular tissue by treatment of ovariectomized ewes with oestradiol and progesterone, and in intercaruncular tissue by oestradiol treatment only.

A technique has been developed for the study of placetal steroid synethesis in tissue culture. Explants of sheep placentas recovered in the last third of gestation produced progesterone and converted labelled androstenedione into unconjugated and conjugated oestrogens. Cortisol added to the medium stimulated 17 alpha-hydroxylase and aromatizing enzyme activities. The results are discussed in relation to the proposal that the rise in secretion of fetal cortisol before parturition has a direct effect on the activation of placental enzymes catalysing the conversion of progesterone to eostrogens.

Parturition in the guinea-pig is not preceded by any consistent change in the maternal plasma concentrations of progesterone, total unconjugated oestrogens or corticosteroids, or by a significant change in the concentration of progesterone-binding globulin (PBG). The onset of parturition was delayed by high doses of oestrogens (stilboestrol and oestradiol), but was not affected by oestriol or an antiserum raised against oestradiol. Premature parturition was achieved by the intra-carotid infusion of adrenocorticotrophin or prostaglandins (PGF2\g=a\, PGE2, I.C.I. 80,996) in conscious animals with indwelling catheters. I.C.I. 80,996, a potent analogue of PGF2\g=a\, induced parturition in all seven guinea-pigs treated; delivery occurred within 6 h of starting the infusion in six animals, and within 48 h in the seventh. The undesirable side-effects that accompanied treatment with PGF2\g=a\ or PGE2 were not encountered with I.C.I. 80,996. Parturition induced experimentally resembled normal delivery but was not preceded by any significant change in the maternal levels of progesterone, total unconjugated oestrogens, corticosteroids, PBG or CBG in the circulation. Oxytocin was not detected until the delivery of the first foetus.Parturition was not induced by maternal or foetal injections of corticosteroids or dexamethasone. Earlier findings are confirmed that the foetal adrenal grows steadily throughout late pregnancy and, unlike the foetal lamb adrenal, undergoes no rapid phase of growth immediately before term. Foetal adrenal weight decreased relative to foetal body weight.The trigger for parturition in this species remains unidentified.