The glycoprotein hormone FSH comes in many different isoforms. In humans and rats the charges of the FSH isoforms vary with reproductive state and these affect the half-life of FSH in plasma. In this study we examined the charge heterogeneity of FSH in pituitary extracts from sheep with different reproductive states. Also the half-life of clearance of pituitary FSH from the different reproductive states was determined in mice. Pituitaries were collected from: anoestrous, luteal phase, follicular phase, early-pregnant and late-pregnant ewes, ewe lambs, ram lambs, rams during the breeding and non-breeding seasons and wethers (5 per group). After extraction, FSH isoforms were fractionated by HPLC anion exchange chromatography. The volume at which half of the FSH had eluted from the ion exchange column was determined (HP(50)). It was found that FSH isoforms from ewes (HP(50)=96.7+/- 1.3 ml (s.e.m. )) eluted later (P<0.01) than those from rams (HP(50)=82.3+/-1.3 ml) indicating that FSH isoforms in the ewes were more acidic than those from rams. There was a seasonal difference in ewes, with ewes in anoestrus (HP(50)=101.6+/-2.6 ml) having more-acidic (P<0.01) FSH isoforms than the ewes during the oestrous cycle (HP(50)=95.3+/-0.7 ml). There was an effect of age, with the FSH isoforms from cycling ewes (HP(50)=95.3+/- 0.7 ml) being more acidic (P<0.01) than those from ewe lambs (HP(50)=88.3+/-1.9 ml). There was an effect of pregnancy, with late-pregnant ewes (HP(50)=107.3+/- 1.6 ml) having more-acidic FSH isoforms (P<0.05) than those from anoestrous ewes (HP(50)=101.6+/-2.6 ml) and there was an effect of castration with the breeding season rams (HP(50)=80.7+/-1.4 ml) having more-acidic (P<0.05) FSH isoforms than wethers (HP(50)=74.0+/-0.5 ml). The half-life of pituitary FSH from animals in the different reproductive states was found to be negatively correlated with HP(50) (r(2)=0.56, P<0.01). The FSH isoforms from wethers were the least acidic and had the longest half-lives. Collectively, these findings show that in sheep, age, sex and reproductive state are all factors which influence the forms of FSH that are extracted from the pituitary gland. Moreover, these results demonstrate that FSH from sheep with the most-acidic FSH isoforms have the shortest half-life in plasma.

Abstract

GH and IGF-I plasma concentrations were measured in lambs during an acute phase response induced by an intrathoracic injection of yeast. The acute phase response was indicated by reduced feed intake, weight loss and an increase in plasma concentrations of the acute phase protein haptoglobin. Intensive blood sampling on day 1 revealed elevated basal concentrations of GH in the yeast-injected group compared with concentrations in pair weight and ad libitum fed control lambs. This suggests that at the beginning of an acute phase response there is an increase in either GH secretion or the half life of GH. No evidence of a specific GH-binding protein in sheep plasma could be detected. IGF-I concentrations in the yeastinjected group remained constant for 3 days then increased to a peak level at day 6. In contrast, plasma IGF-I concentrations were depressed from days 3 to 6 in the pair weight control group and they were unchanged in the ad libitum fed controls. When the IGF-I concentrations were elevated in the yeast-injected group, this group had a higher daily weight gain despite their lower feed intake compared with the ad libitum fed controls. These results suggest that IGF-I may be associated with the increase in weight in the late stage of an acute phase response during recovery from an infection or injury. Day 1 GH peak amplitude concentrations in the yeast-injected lambs were negatively correlated with IGF-I concentrations on the following 2 days yet in the pair weight lambs the correlation was in a positive direction suggesting that the relationship between GH and IGF-I is different between animals that lose weight during an acute phase response and animals that lose weight because of feed restriction.

Journal of Endocrinology (1995) 144, 243–250

Abstract

The aim of this study was to examine the effect of the FecB^B fecundity gene on plasma concentrations and pituitary content of growth hormone (GH) in sheep. No differences were found between homozygous carriers (BB) and non carriers (++) of the FecB^B gene with regard to pituitary GH contents in both ovariectomized and intact ewes. However, ovariectomized ewes had higher levels of pituitary GH than intact ewes (P<0·01). There were no differences between FecB^B genotypes with respect to plasma concentrations of GH in 6-year-old ovariectomized ewes bled every 10 min for 12 h or in ram lambs bled weekly during their first year of life. GH levels in the rams decreased until week 27, increased to a peak at week 31 then decreased before increasing again at week 43. Mean plasma GH concentrations in the ewe lambs bled weekly for a year decreased until week 19 then remained at approximately this level for the remainder of the year. Mean GH plasma concentrations in the ram lambs were higher than in the ewe lambs (P<0·001). Ewe lambs that were homozygous for the FecB^B gene had lower body weights (P<0·05) and had higher levels of GH (P<0·01) than non carrier ewe lambs during their first year. Before the average age of first behavioural oestrus (36 weeks) GH levels in the ewe lambs were negatively correlated with body weights (r=−0·69, P<0·001, n=22). When body weight was included as a covariate in analysis of variance the genotype difference in ewe lamb plasma GH concentrations was no longer significant. In summary, pituitaries from ovariectomized ewes had higher levels of GH than those from intact ewes. There were no FecBB gene specific differences in pituitary levels of GH, the profile of plasma GH in 6-year-old ovariectomized ewes or in ram lambs during their first year of life. BB ewe lambs had higher levels of GH than ++ ewe lambs during their first year; however, this difference was probably due to the BB ewes having lower body weights than the ++ ewes because body weight was negatively correlated with mean GH levels.

Journal of Endocrinology (1995) 147, 217–223