Pituitary Content of Gonadotropins and GnRH-Receptors in Pregnant, Postpartum and Steroid-Treated OVX Ewes

Crowder, M. E.; Gilles, Pamela A.; Tamanini, Carlo; Moss, G. E.; Nett, Terry M.

doi:10.2527/jas1982.5461235x

Cited by 47 publications

(20 citation statements)

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“…The relationship between circulating LH concentrations and the number of pituitary gland GnRH receptors has been studied extensively in the rat, in which changes in circulating gonadotropin concentrations occur in association with changes in the number of GnRH receptors in the pituitary gland (reviewed in [9,32]). Similar quantitative changes have been documented in other species including primates and sheep [41,43,44].…”

Section: Discussionsupporting

confidence: 50%

Extra- and Intracellular Effects of Divergent Selection for Pituitary Responsiveness to Gonadotropin-Releasing Hormone in Prepubertal Ram Lambs1

Evans

Bramley

McNeilly

et al. 1997

Biology of Reproduction

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Divergent selection based on the response of 10-wk-old male lambs to a GnRH challenge has produced two lines of sheep, referred to as high and low lines, that differ in their ability to release LH in response to pharmacological and physiological doses of GnRH. The aim of this study was to determine whether the between-line differences in pituitary sensitivity were related to differences in GnRH receptor number and/or the transduction of the intracellular signal following GnRH receptor activation. Pituitary glands were collected from fourteen 20-wk-old ram lambs from each line, weighed, and sampled for GnRH receptor analysis. The remaining tissue from 9 lambs from each line was dispersed. Of the resultant cell suspension, a sample was stored for measurement of GnRH receptor content and the remainder was plated and cultured for 24 h. The LH responses of cultured cells were measured after exposure to GnRH, A23187, or the phorbol ester phorbol 12,13 dibutyrate (PDB). The results indicated that the pituitary glands of the high line contained significantly higher concentrations of GnRH receptors than did those of the low line and released significantly more LH after stimulation with either GnRH or the Ca2(+)-calmodulin or protein kinase C intracellular second messenger systems. Therefore, the between-line difference in the regulation of pituitary LH secretion occurs at a step distal to the stimulatory sites of action of A23187 and PDB.

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Section: Discussionsupporting

confidence: 50%

Extra- and Intracellular Effects of Divergent Selection for Pituitary Responsiveness to Gonadotropin-Releasing Hormone in Prepubertal Ram Lambs1

Evans

Bramley

McNeilly

et al. 1997

Biology of Reproduction

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“…In ovariectomised ewes treated (for a period equivalent to that of gestation) with a daily dose of oestradiol equivalent to that which occurs during gestation, there is a progressive reduction in the amount of LH released following GnRH injection and also a fall in pituitary LH, both these parameters being directly correlated. Simultaneously there was an increase in the number of GnRH receptors in the pituitary (Crowder et al, 1982 (Tang, 1977).…”

mentioning

confidence: 99%

Endocrine regulation of postpartum ovarian activity in cattle : a review

Hanzen

1986

Reprod. Nutr. Dévelop.

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Summary. The Clinically, the postpartum period is characterized by a period of behavioural anoestrus, the duration of which differs in different breeds.If the detection of oestrus is optimal, anoestrus lasts for 20 to 70 days in dairy cows Callahan et al., 1971 ;Schams et al., 1978 ;Pirchner et al., 1983 ;Richardson et al., 1983 ;Etherington et al., 1984). This period is highly variable in suckled cows and lasts from 30 to 110 days (Wiltbank and Cook 1958 ;Oxenreider 1968 ;Graves et al., 1968 ;Casida et al., 1968 ; Nancarrow et al., 1977 ;Holness et al., 1978 ;Wettemann et a/., 1978 ;Short et al., 1979 ;Dunn and Kaltenbach, 1980 ;Kesler et al., 1980 ;Randel, 1981 ;Montgomery, 1982 ;Peters and Riley, 1982 . Jainudeen et al., 1982Bastidas et al., 1984 ;King and Mc Leod, 1983Leod, /1984Hansen and Hauser, 1984 ;Montgomery et al., 1985).Assay of progesterone in plasma or milk has shown that 88 % of animals of dairy breeds have an luteal activity present by 35 days after calving (Ball and Lamming, 1983) and 95 % within 50 days (Bulman and Lamming, 1978). According to different authors, the first rise of progesterone appears between 16 and 69 days after calving in dairy cows (Webb et al., 1977(Webb et al., , 1980Pirchner et al., 1983) and between 56 and 96 days in suckled cows (Fonseca et al., 1980 ;Peters and Riley 1982 ; Jainudeen et al., 1982 Jainudeen et al., /1983Montgomery et al., 1985).It is possible to detect ovarian follicles by rectal palpation in both milked and suckled cow from the second week after calving (Saiduddin et al., 1968 ;Callahan et al., 1971 ;Kesler et al., 1979 ;Webb et al., 1980 ;Kesler et al., 1980 ;Stevenson et al., 1983 (Wiltbank et al., 1962(Wiltbank et al., , 1964Dunn et al., 1969 ; Lammond, 1970 ;Corah et al., 1975 ;Whitman et a/., 1975 ;Duffour, 1975 ;Holness et al., 1978 ;Carstairs et al., 1980 ;Dunn and Kaltenbach, 1980 ; Gauthier and Thimonnier, 1982 ;Peters and Riley, 1982 ; Mc Leod, 1983/1984 ;Rutter and Randel, 1984). Some authors have found that overfeeding improves ovarian (Wiltbank et al., 1962(Wiltbank et al., , 1964Hansen et al., 1982) or pituitary (Beal et al., 1978 ;Jordan and Swanson, 1979 ;Lishman et al., 1979 ;Moss et al., 1982) function. Others have found no relation between feeding and the ovarian (Lishman et al., 1979 ;Carstairs et al., 1980) or pituitary (Hill et a/., 1970 ;Dunn et al., 1974 ;Spitzer et al., 1978 ;Haresign, 1981 ;Rutter and Randel, 1984) activity.Little is known about the mechanism under which diet exerts its effect. It is conceivable that feeding influences the ovarian response to gonadotropins (Gombe and Hansel, 1973). There was a positive correlation between the degree of fatness of an animal and the plasma concentration of 17 !3-oestradiol, 7 weeks after calving (Lishman et al., 1979).Feeding affects the release of luteinizing hormone (LHI and subsequent luteal function Spitzer et al., 1975 ;Apgar et al., 1975 ;Beal et al., 1978). It has been observed that the release of LH induced by gonadotropin releasing hormone (GnRH) injection was grea...

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“…Before the ovulatory LH surge, during pro-oestrus, there is an increase in Gn-RH levels in the median eminence, and this is accompanied by an increase in pituitary LH content (Roche, Foster, Karsch, Cook & Dziuk, 1970 ;Crighton, Hartley & Lamming, 1973 ;Wheaton, 1979 (Chamley, Jonas & Parr, 1976 (Jenkins et al, 1977;Wright et al, 1980;Crowder et al, 1982) Prolactin secretion in post-partum anoestrous ewes was greater than that in seasonally anoestrous ewes, as found by others (Lamming et al, 1974;Kann & Denamur, 1974). Pituitary prolactin content was similar in both groups, indicating that the greater secretion postpartum is due to greater synthesis of prolactin.…”

Section: Oestrogen Receptorsmentioning

confidence: 99%

“…Pituitary responsiveness to gonadotrophin-releasing hormone (Gn-RH) declines during pregnancy (Chamley, Findlay, Cumming, Buckmaster & Goding, 1974) and is lower in post-partum ewes lambing during the breeding season than in dioestrous ewes (Wright et al, 1980). Jenkin, Heap & Symons (1977) and Crowder, Gilles, Tamanini, Moss & Nett (1982) have reported poor responsiveness to Gn-RH 1 day after parturition but this may return to normal within 11 days (Crowder et al, 1982) to 3 weeks (Jenkin et al, 1977) if ewes do not suckle. Pituitary LH content is restored soon after parturition (Jenkin et al, 1977;Crowder et al, 1982).…”

Section: Introductionmentioning

confidence: 99%

“…Jenkin, Heap & Symons (1977) and Crowder, Gilles, Tamanini, Moss & Nett (1982) have reported poor responsiveness to Gn-RH 1 day after parturition but this may return to normal within 11 days (Crowder et al, 1982) to 3 weeks (Jenkin et al, 1977) if ewes do not suckle. Pituitary LH content is restored soon after parturition (Jenkin et al, 1977;Crowder et al, 1982).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Differences in the reproductive endocrine status of ewes in the early post-partum period and during seasonal anoestrus

et al. 1984

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Summary. More (P < 0\m=.\05)post-partum acyclic ewes (8/9) showed evidence of pulsatile LH release than did seasonally anoestrous ewes (2/8). Mean These data suggest that the basis of acyclicity in seasonally anoestrous ewes and in post-partum ewes is probably due to their inability to generate LH pulse frequencies similar to that in the follicular phase of the oestrous cycle. The higher LH pulse frequency in post-partum ewes, compared to that in seasonally anoestrous ewes, suggests that pregnancy may partly negate the reduction in LH secretion that is associated with photoperiod-induced acyclicity. The lower number of nuclear-bound oestrogen receptors in post-partum ewes suggests that there may be lower plasma oestrogen levels and less ovarian follicular growth than in non-suckling anoestrous ewes.

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Pituitary Content of Gonadotropins and GnRH-Receptors in Pregnant, Postpartum and Steroid-Treated OVX Ewes

Cited by 47 publications

References 0 publications

Extra- and Intracellular Effects of Divergent Selection for Pituitary Responsiveness to Gonadotropin-Releasing Hormone in Prepubertal Ram Lambs1

Extra- and Intracellular Effects of Divergent Selection for Pituitary Responsiveness to Gonadotropin-Releasing Hormone in Prepubertal Ram Lambs1

Endocrine regulation of postpartum ovarian activity in cattle : a review

Differences in the reproductive endocrine status of ewes in the early post-partum period and during seasonal anoestrus

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