The roe deer blastocyst is in diapause between August and December, after which time it expands and elongates rapidly before implantation. Blood samples were taken from 30 animals to define temporal changes in reproductively important hormones to investigate the physiological cues present at embryo reactivation. In 15 of these animals, changes in uterine and conceptus protein synthesis and secretion, and luteal progesterone release during diapause and reactivation, were assessed after culture of these tissues in vitro. Oestradiol concentrations remained low during diapause (1.07 +/- 0.4 pg ml(-1)) and expansion (1.2 +/- 0.4 pg ml(-1)) but increased by 30 times at trophoblast elongation (49.17 +/- 0.37 pg ml(-1)). Prolactin remained at basal concentrations (4.69 +/- 0.86 ng ml(-1)) and increased after implantation (12.34 +/- 2.71 ng ml(-1)). Peripheral progesterone concentrations and luteal progesterone release remained constant throughout diapause, reactivation and implantation (peripheral progesterone: 3.82 +/- 1.97 ng ml(-1); luteal progesterone: 6.72 +/- 0.81 ng mg(-1) protein). Incorporation of a radiolabel into conceptus secretory proteins increased by four times at expansion compared with diapause, whereas incorporation into endometrial secretions remained constant. At elongation, incorporation into endometrial secretions increased two times and conceptus secretions increased 32 times. Two-dimensional electrophoresis and fluorography showed that the profile of endometrial secretory proteins was constant until implantation when qualitative changes were evident. Although a role for an endocrine maternal trigger of reactivation from diapause cannot be dismissed, these data provide no supporting evidence and indicate that the conceptus itself may drive reactivation.
RT Lambert, CJ Ashworth, L Beattie, FE Gebbie, JS Hutchinson, DJ Kyle and PA Racey
P Da Silva, RP Aitken, SM Rhind, PA Racey and JM Wallace
The influence of maternal nutrition during pregnancy on anterior pituitary gonadotrophin gene expression and ovarian development in sheep fetuses during late gestation was investigated. Embryos recovered from superovulated adult ewes that had been inseminated by a single sire were transferred, singly, into the uteri of adolescent recipients. After embryo transfer, adolescent ewes were offered a high or moderate amount of a complete diet. Pregnancies were terminated at day 131 +/- 0.6 of gestation and the fetal brain, anterior pituitary gland and gonads were collected. Gonadotrophin gene expression (LHbeta and FSHbeta subunits) in the fetal pituitary gland was examined using in situ hybridization. Ovarian follicular development was quantified in haematoxylin- and eosin-stained ovarian sections embedded in paraffin wax. Six dams that were offered a high nutrient intake carried normal-sized fetuses (weight within +/- 2 SD of mean weight for control fetuses from dams fed a moderate level of complete diet) and 13 dams carried growth-restricted fetuses (weight +/- 2 SD of mean weight for control fetuses from dams fed a moderate level of complete diet). Mean placental masses in these groups were 354 +/- 24.5 and 230 +/- 21.1 g, respectively, compared with 442 +/- 54.3 g in the dams that were offered a moderate nutrient intake (n = 6). Growth-restricted fetuses from dams offered a high nutrient intake showed higher pituitary LHbeta mRNA expression (P < 0.05) than normal-sized fetuses from dams offered a moderate nutrient intake (252 +/- 21.6 and 172 +/- 23.6 nCi g(-1), respectively). FSHbeta mRNA expression was not influenced by growth status. Fewer follicles (primarily in the resting pool) were observed in the ovaries of both growth-restricted (P < 0.002) and normal-sized fetuses from dams offered a high nutrient intake (P < 0.01) compared with normal-sized fetuses from dams offered a moderate nutrient intake. Irrespective of nutritional treatment, the total number of follicles was positively associated with placental mass (P < 0.01). Thus, a high maternal nutrient intake during adolescent pregnancy had a negative influence on ovarian follicular development in fetuses as determined during late gestation.
P Da Silva, RP Aitken, SM Rhind, PA Racey and JM Wallace
The onset of puberty in prenatally growth-restricted versus normally grown lambs of both sexes, born in April and housed under natural photoperiod, was examined. Singleton pregnancies were established and adolescent ewes were offered a high or moderate nutrient intake throughout gestation. Placental mass was reduced (P < 0.001) in high compared with moderate intake dams and resulted in the birth of growth-restricted and normal birth weight offspring, respectively. At birth, female lambs weighed 3.43 kg versus 5.03 kg (P < 0.001; n = 14 per group) and male lambs weighed 2.75 kg versus 5.18 kg (P < 0.001; n = 7 per group) in growth-restricted and normal birth weight groups, respectively. Lambs suckled for 12 weeks and thereafter were fed ad libitum until week 43 of age. Growth-restricted lambs had lower preweaning live weight gains and this difference was more pronounced in male (P < 0.05) than in female lambs (P = 0.07). Thereafter, live weight remained lower (P < 0.05) in growth-restricted than in normally grown lambs of both sexes until week 25 of age. In females, the time of onset of puberty was similar in the two groups. All females ovulated and there were no differences in the number of ovarian cycles recorded or in the incidence of aberrant ovarian function. In males, testosterone concentrations and testicular volume were lower in growth-restricted compared with normally developed lambs from birth until weeks 28 and 35 of age, respectively (P < 0.05). The seasonal increase in plasma testosterone concentrations occurred later in growth-restricted than in normally developed lambs (P < 0.01) but the timing of maximum peak concentrations was similar. Peak testosterone concentrations were lower (P < 0.05) in growth-restricted than in normal male lambs.