Within-breed artificial insemination and between-breed embryo transfer were carried out in small pony (P) and large Thoroughbred (Tb) mares to create 4 types of horse pregnancy in which the fetus experienced spatial and nutritional deprivation (Tb-in-P; n=8), luxury (P-in-Tb; n=7) or normality (Tb-in-Tb; n=7 and P-in-P; n=7) in utero. Measurement of equine chorionic gonadotrophin (eCG), total conjugated oestrogens and progestagen concentrations in serial peripheral serum samples recovered from all the mares throughout gestation showed that the amount of eCG produced during the first half of gestation was dependent upon the breed of the mare rather than the breed of the fetus being carried. In contrast, the mean total amounts of oestrogens produced, as measured by area under the curve, were significantly greater (P=0.003) in the two types of pregnancy in which a Thoroughbred fetus was being carried (Tb-in-Tb and Tb-in-P) than those in which a pony fetus was gestated (P-in-P and P-in-Tb); the evidence suggests that the Tb fetus may have larger gonads than the P fetus and thereby secrete more C-19 precursor steroids for aromatisation to oestrogens by the placenta. In the final weeks of pregnancy mean plasma progestagen concentrations rose much earlier, and to significantly higher levels (P<0.001), in the Tb-in-P than in the P-in-Tb pregnancies, thereby reflecting the increased fetal stress in the former causing premature maturation of the fetal adrenal gland. This, in turn, resulted in increased secretion of pregnenolone by the adrenal cortex for conversion to progestagens by the placenta.
WR Allen, S Wilsher, F Stewart, F Stewart, J Ousey, J Ousey and A Fowden
F. Stewart, J. A. Goode and W. R. Allen
A heterologous radioimmunoassay was developed and validated for the measurement of horse GH in plasma. It utilized recombinant-derived bovine GH as the radiolabelled ligand, a guinea-pig anti-porcine GH serum as first antibody and pituitary-derived horse GH as standard. Cross-reactivites were high with all of the pituitary and recombinant-derived GH preparations tested (49–140%) and very low (<0·3%) with horse FSH, LH and prolactin. A synthetic analogue of GH-releasing factor(1–29) stimulated the expected pattern of GH release in foals.
Plasma GH concentrations in foals were low at birth (<20 ng/ml) but rose sharply to a definite and, in most cases, very large peak (18–195 ng/ml) during the first 30–40 min post partum, followed by a steady decline to basal levels again by 60–100 min post partum. GH secretion was clearly pulsatile in all older foals tested (2 weeks, 1 month and 4 months of age) and in six adults (three mares and three stallions), all bled at 15-min intervals for 7–8 h. Basal levels and pulse amplitudes were higher in foals than in adults and pulse frequency was higher in stallions than in mares (3–5 pulses/8 h vs 1–2 pulses/8 h). Pulsatile secretion was further characterized in one mare by simultaneous sampling of jugular vein and pituitary cavernous sinus blood. Peak GH concentrations in cavernous sinus blood draining the pituitary gland were more than tenfold higher than the corresponding peak concentrations in peripheral circulation. The patterns of GH release in the horse therefore appear to be similar to those reported in other species with the exception of the low values at birth followed by the dramatic rise and fall in concentrations during the first hour post partum.
Journal of Endocrinology (1993) 138, 81–89
M Chopineau, N Martinat, C Troispoux, H Marichatou, Y Combarnous, F Stewart and F Guillou
Horse (Equus caballus) luteinizing hormone (eLH) and chorionic gonadotrophin (eCG), which have the same amino acid sequence, are unusual in that, although they express only LH activity in equids, they express dual LH and FSH activities in all other species tested. Donkey (Equus asinus) LH (dkLH) and CG (dkCG), which also share an identical peptide backbone, have been less well characterized and conflicting results concerning their FSH activity in heterologous species have appeared in the literature. In order to assess and compare the intrinsic LH and FSH activities of the horse and donkey LHs in heterologous species, recombinant eLH (r.eLH/CG) and recombinant dkLH (r.dkLH/CG) were expressed, for the first time, in COS-7 cells. Their LH activities were assessed in a rat Leydig cell bioassay, and their FSH activities were estimated in a bioassay using Y1 cells stably expressing the human FSH receptor. Human CG (hCG) was expressed (r.hCG) and analysed in the same system. The results showed that, whereas r.dkLH/CG was about twice as active as r.eLH/CG in the LH bioassay, it was five times less active than r.eLH/CG in the FSH bioassay; r.hCG was about three times less active than r.eLH/CG in the LH bioassay but was completely inactive in the FSH bioassay. These results confirm that dkLH/CG possesses significant FSH activity in heterologous species that is not attributable to contamination with FSH.
Journal of Endocrinology (1997) 152, 371–377
HELEN J. STEWART, E. A. BENSON, M. MAUREEN ROBERTS, A. P. M. FORREST and F. C. GREENWOOD
Plasma growth hormone (GH) levels during insulin hypoglycaemia were measured in 30 women with implants of 90Y in the pituitary for advanced breast cancer. There was evidence of continued pituitary activity in six patients (20%), the rise in plasma GH level being greater than 4 ng/ml during hypoglycaemia. Thirteen patients (43%) were regarded as having complete ablations because they had no GH response and a fasting level of less than 4 ng/ml. In the remaining 11 patients (37%) there was no rise in the GH level during hypoglycaemia, but there were significant fasting levels. From the post-mortem evidence it was concluded that these patients also had adequate ablations.
This test is shown to be of more value in estimating residual pituitary function than routine tests of thyroid or adrenal function.
F. Stewart, J. A. Thomson, S. E. A. Leigh and J. M. Warwick
Several cDNA clones corresponding to mRNA for the α-subunit of the horse (Equus caballus) pituitary and placental (chorionic) gonadotrophic hormones have been isolated and sequenced. Polyadenylated mRNA was purified from horse pituitary glands (the source of FSH and LH) and horse placental tissues (the source of chorionic gonadotrophin; CG). The mRNA preparations were characterized by in-vitro translation and Northern hybridization techniques using human and ovine gonadotrophin cDNA clones as probes. Complementary DNA libraries were created from the pituitary and placental mRNAs and a human CG α-subunit probe was used to isolate several horse α-subunit cDNA clones. The α-subunit nucleotide sequence from both sources of tissue was identical, thereby indicating that in the horse (as in man) the same gonadotrophin α-subunit gene is expressed in the pituitary and placenta. Our results are consistent with transcription of a single α-subunit gene for all the glycoprotein hormones in the horse, and we suggest that the reported differences between the horse CG and FSH α-subunit amino acid sequences determined by conventional peptide sequencing methods arose due to errors in the FSH α-subunit sequence. Comparison of the deduced amino acid sequence of the horse α-subunit with that of other α-subunit sequences indicated a number of significant differences which may be related to the unusual receptor-binding properties of the equine gonadotrophins.
J. Endocr. (1987) 115, 341–346
S. R. Crosby, M. F. Stewart, W. E. Farrell, S. Gibson and A. White
The molecular forms of ACTH secreted by established human small cell lung cancer (SCLC) cells and primary cultures derived from a bronchial carcinoid tumour, a pituitary adenoma and hyperplastic pituitary tissue have been characterized by Sephadex G-75 chromatography and quantified with two novel immunoradiometric assays for ACTH and ACTH precursor peptides. Pro-opiomelanocortin (POMC; M r 31 000) and pro-ACTH (M r 22 000) were secreted by all cell types. No smaller peptides were identified in the culture media from SCLC and bronchial carcinoid cells, implying a deficiency in the enzymes and/or intracellular organelles required for extensive POMC processing. A more heterogeneous profile of ACTH-containing peptides was produced by cells of pituitary origin, indicating more extensive proteolytic processing of POMC. However, the major peptide secreted by cells from a large aggressive pituitary adenoma was unprocessed POMC (M r 31 000). These results suggest that both lung and pituitary cells in vitro retain their in-vivo pattern of POMC processing and provide valuable models in which to study the regulation of ACTH synthesis and secretion.
Journal of Endocrinology (1990) 125, 147–152
P R Riley, D R E Abayasekara, H J Stewart and A P F Flint
The entire coding region of an ovine endometrial oxytocin receptor (OTR) cDNA was generated by PCR, subcloned into the SV40 major late promoter expression vector pSVLJ and transiently expressed in Cos-7 cells. A specific OTR antagonist, 125I-labelled d(CH2)5 [Tyr(Me)2,Thr4,Tyr-NH2 9]-vasotocin (OTA), was used to describe the binding kinetics of the expressed receptor which had a K d of 4·5 nm and Bmax of 2·4 nm/mg protein (6·8 × 105 receptor molecules/transfected cell). The functional properties of the expressed OTR were determined by measuring oxytocin-induced phosphoinositide (PI) hydrolysis. Oxytocin increased PI turnover in OTR transfected cells fourfold in excess of residual endogenous activity, and stimulated phospholipase C (PLC) activity in a dose- and time-dependent manner, confirming that the expressed OTR cDNA was functional. Arginine vasopressin also stimulated PI turnover in a dose-dependent manner; thresholds of responses to oxytocin and arginine vasopressin were 10−9 m and 10−7 m respectively. OTA did not increase PI turnover and competitively inhibited the oxytocin-induced response. Direct activation of the pathway by aluminium fluoride and guanosine (3′-Othio)-triphosphate (GTPγS) confirmed that the OTR was G-protein linked. Co-incubation of GTPγS with oxytocin shifted the PI-response threshold from 10−7 m to 10−9 m and significantly increased the level of response, suggesting that maximum PI turnover was agonist-dependent. The G-protein involved in mediating the signal transduction pathway was pertussis toxin-insensitive and, therefore, probably a member of the Gq subfamily. The PLC inhibitor, U73122, had no effect on oxytocin-induced PI turnover, consistent with the response in endometrial tissue. These data suggest that the signalling pathway mediated by expressed OTR is similar to that attributed to OTR occupancy in ovine endometrium.
Journal of Endocrinology (1996) 149, 389–396
M Chopineau, N Martinat, H Marichatou, C Troispoux, C Auge-Gouillou, F Stewart, Y Combarnous and F Guillou
Horse LH/chorionic gonadotrophin (eLH/CG) exhibits, in addition to its normal LH activity, a high FSH activity in all other species tested. Donkey LH/CG (dkLH/CG) also exhibits FSH activity in other species, but about ten times less than the horse hormone. In order to understand the molecular basis of these dual gonadotrophic activities of eLH/CG and dkLH/CG better, we expressed, in COS-7 cells, hybrids between horse and donkey subunits, between horse or donkey alpha-subunit and human CG beta (hCG beta), and also between the porcine alpha-subunit and horse or donkey LH/CG beta. The resultant recombinant hybrid hormones were measured using specific FSH and LH in vitro bioassays which give an accurate measure of receptor binding specificity and activation. Results showed that it is the beta-subunit that determines the level of FSH activity, in agreement with the belief that it is the beta-subunit which determines the specificity of action of the gonadotrophins. However, donkey LH/CG beta combined with a porcine alpha-subunit exhibited no FSH activity although it showed full LH activity. Moreover, the hybrid between horse or donkey alpha-subunit and hCG beta also exhibited only LH activity. Thus, the low FSH activity of dkLH/CG requires an equine (donkey or horse) alpha-subunit combined with dkLH/CG beta. These results provide the first evidence that an alpha-subunit can influence the specificity of action of a gonadotrophic hormone.
T. J. Parkinson, H. J. Stewart, M. G. Hunter, D. S. C. Jones, D. C. Wathes and A. P. F. Flint
Analysis of ovine conceptus RNA by slot blotting, Northern analysis and nested polymerase chain reaction failed to detect oxytocin–neurophysin prohormone mRNA. Probes used hybridized with both the 3' end of the prohormone mRNA and the oxytocin-coding sequence. Northern analysis of bovine and porcine conceptus RNA was also negative, and polymerase chain reaction demonstrated oxytocin–neurophysin mRNA in ovine corpus luteum, but not in human corpus luteum or decidua, or in ovine endometrium. Infusion of oxytocin into the uterine lumen in cyclic ewes between days 9 and 19 or 20 after oestrus failed to prolong the luteal phase of the cycle and had no effect on endometrial oxytocin receptor concentrations or uterine prostaglandin F secretion. Oxytocin administered systematically prevented luteolysis and reduced uterine prostaglandin F secretion. Taken together, these data suggest that blastocyst-derived oxytocin is unlikely to contribute to corpus luteum maintenance in early pregnancy. They are inconsistent with a previous report that the ovine blastocyst synthesizes and secretes oxytocin.
Journal of Endocrinology (1991) 130, 443–449
H.J. Stewart, S.H.E. McCann, P.J. Barker, K.E. Lee, G.E. Lamming and A.P.F. Flint
Sequencing of the 40 N-terminal amino acids of the blastocyst protein responsible for blocking corpus luteum regression in early pregnancy in sheep revealed a 37% homology with human α-interferon; 28% of the remaining amino acid changes were conservative. 125I-Labelled human α-interferon bound to membrane receptors from sheep uteri with an approximate Kd of 4 × 10−11 M; binding was inhibited by unlabelled α-interferon or purified blastocyst antiluteolytic protein. The blastocyst antiluteolytic protein therefore closely resembles the interferon-α family of antiviral proteins.