oestrogen - Reproduction

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Bedford, CA., Harrison, F.A. & Heap, R.B. (1972). The metabolic clearance rate and production of pro¬ gesterone and the conversion to 20a-hydroxypregn-4-.
Comparison of LH release and luteal function in cyclic and LH-RH-treated anoestrous ewes pretreated with PMSG or oestrogen W.

Haresign

and G. E.

Lamming

Department of Physiology and Environmental Studies, University ofNottingham School of Agriculture, Sutton Bonington, Loughborough, Leics LE12 5RD, U.K.

Summary. Pretreatment of seasonally anoestrous Clun Forest ewes with 750 i.u. PMSG or 50 \g=m\g oestradiol benzoate 24 or 7 h respectively before a single injection of 150 \g=m\g synthetic LH-RH significantly increased the release of LH compared to that after injection of 150 \g=m\g LH-RH alone. Total LH release in the two 'combined' treatments was approximately 70 % of that found at a natural oestrus, compared to 25 % for LH-RH alone. All but one of the treated ewes ovulated, but only those pretreated with PMSG consistently produced corpora lutea capable of elevating peripheral plasma progesterone concentrations although these were lower than those at natural mid-cycle. These progesterone concentrations were, however, comparable to those during the natural cycle when corrected for the higher metabolic clearance rate found during anoestrus.

Introduction

Administration of a single injection of 150 µg LH-RH to seasonally anoestrous Clun Forest ewes in¬ duced LH release in all animals and ovulation in the majority, although luteal function, as assessed by peripheral plasma progesterone concentrations, was completely absent in most of the treated animals (Haresign, Foster, Haynes, Crighton & Lamming, 1975). Since the LH release was significantly lower than that observed at a natural oestrus (Foster & Crighton, 1975) it was suggested that the lack of luteal function might be due to an inadequate LH release before ovulation. Attempts to augment the induced LH release by increasing the dose of LH-RH to 300 µg failed (Haresign et al, 1975). Simultaneous determination of LH and LH-RH-like activity in jugular venous plasma of ewes at oestrus (Crighton, Foster, Holland & Jeftcoate, 1973) suggested that administration of the LH-RH as a series of injections might simulate the natural preovulatory LH peak more closely. When this pro¬ cedure was followed there was a significant increase in the induced LH release, and ovulation occurred but the subsequent peripheral plasma progesterone concentrations remained basal (Crighton, Foster, Haresign & Scott, 1975). Reeves, Arimura & Schally (1971a, b) have reported that pituitary response of seasonally anoestrous ewes is augmented by pretreatment with exogenous oestrogen before admin¬ istration of LH-RH, but no details of luteal function were given. Rises in peripheral plasma progesterone concentration, similar to those found during the oestrous cycle, oestrus and LH release were obtained in seasonally anoestrous ewes treated with PMSG and synthetic progestagens (Lintin, Lamming & Butt, 1973). The present study was an examination of the LH and progesterone profiles in seasonally anoes¬ trous ewes treated with LH-RH alone and in conjunction with PMSG or oestradiol benzoate. These were compared to the changes occurring during a natural oestrous cycle in an attempt to understand the lack of luteal function in ewes treated with LH-RH alone. * Present address: Department of Agriculture and Horticulture, Sutton Bonington, Loughborough, Leics LE12 5RD, U.K.

University of Nottingham School of Agriculture,

Materials and Methods Animals and experimental design Thirteen

seasonally anoestrous ewes were treated 2 weeks after weaning at the beginning of June (Groups 1-3) and 5 untreated cyclic ewes were used in November (Group 4) at the height of the breeding season. All ewes were housed under conditions of natural daylength and temperature throughout the experiment and were checked for oestrus twice daily with a vasectomized ram. Treatment of the anoestrous ewes consisted of a single intravenous (i.v.) injection of 150 µg syn¬ thetic LH-RH (Hoechst) alone (5 ewes: Group 1), a single intramuscular (i.m.) injection of 50 µg oestradiol benzoate (Sigma Chemical Co., St Louis, U.S.A.) in arachis oil followed 7 h later by a single i.v. injection 150 µg synthetic LH-RH (4 ewes: Group 2), or a single subcutaneous (s.c.) in¬ jection 750 i.u. PMSG (Schering, Berlin, W. Germany) followed 24 h later by a single i.v. injection of 150 µg synthetic LH-RH (4 ewes : Group 3). Preliminary investigations had shown that LH release began 130 ± 1-5 (s.e.m.) h after oestradiol benzoate injection and 34-0 ± 30 h after PMSG injection (W. Haresign, unpublished data). Blood samples for progesterone determination were collected daily by jugular venepuncture for 2 days before and 20 days after treatment from the seasonally anoestrous ewes and for a complete oestrous cycle, commencing on the day of oestrus (Day 0), from the cyclic ewes. Samples for LH determinations were collected from an indwelling jugular vein cannula at 15-min intervals for 1 h be¬ fore and 7 h after administration of LH-RH to the anoestrous ewes and every 15 min for 18 h after the onset of oestrus in the cyclic ewes. All blood samples were centrifuged at 1600 g· and 4°C for 15 min and the resultant plasma was stored at —20°C until assayed. All ewes were subjected to laparotomy for examination of the reproductive tract on the 3rd day after treatment of ewes in Groups 1-3 or on Day 3 of the cycle (Group 4).

Assays Progesterone. Plasma progesterone concentrations were determined by the radioimmunoassay previously described (Haresign et al, 1975). There was negligible cross-reaction with any of the major steroids occurring in ovine plasma. Sensitivity of the assay was 26 pg/tube (0-08 ng/ml plasma); the inter- and intra-assay coefficients of variation were