The acute effect of oestrogen injection on plasma LH in freemartin heifers

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Injection of oestradiol was followed by a surge of plasma LH within 24 h in only 7 of 12 freemartins. Elevations of plasma LH were less than those reported for normal non-cyclic heifers, but some freemartins showed a delayed, or more prolonged, LH response. Responsiveness to oestradiol was not related to degree of chimaerism or plasma androstenedione level, and most of the animals responded similarly in two trials carried out 4 months apart, during which time plasma androstenedione levels had more than doubled. Freemartins which showed an LH surge after oestradiol treatment released greater amounts of LH after the injection of LH-RH than did non-responders.

Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

The acute effects of oestradiol-17 and synthetic LH-RH on plasma LH levels in freemartin heifers

Cunningham¹,

Saba²,

Boarer³

1977

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“…However, this apparent independence of the tonic levels of plasma LH and FSH is replaced by a close association of surges of both hormones at oestrus or when provoked by oestrogen, LH-RH, or progesterone-implant removal (Reeves et alIn marked contrast, plasma gonadotrophin concentrations in the mature ram show episodic fluctuations in plasma LH, which are not correlated with changes in FSH levels (Katongole, Naftolin & Short, 1974;Lee et al, 1976a). This difference between ewes and rams is also evident in the response to LH-RH; the mature ram shows an increase in plasma LH but very little or no increase in plasma FSH concentrations (Hopkinson, Pant & Fitzpatrick, 1974;Lee et al, 1976b).Following observations on the effect of oestrogen on plasma LH concentrations in freemartin sheep and heifers (Short, 1974;Saba, Symons, Cunningham & Boarer, 1976) which suggested that responses could be of the male or female type, it was of interest to determine the pattern of plasma hormone levels in freemartin sheep. This paper presents data on some plasma hormones in a mas¬ culinized freemartin ewe, its male sibling, three normal rams, and four wethers.…”

mentioning

confidence: 98%

Plasma gonadotrophin and androgen concentrations in a freemartin ewe and its male sibling

Saba¹,

Cunningham²,

Boarer³

1977

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Investigations of plasma gonadotrophin concentrations in intact ewes have shown that, in general, LH concentrations are low and fairly stable whereas FSH levels, which are much higher, may fluctuate from 15 ng to over 100 ng FSH/ml (Salamonsen et al., 1973). However, this apparent independence of the tonic levels of plasma LH and FSH is replaced by a close association of surges of both hormones at oestrus or when provoked by oestrogen, LH-RH, or progesterone-implant removal (Reeves et al.In marked contrast, plasma gonadotrophin concentrations in the mature ram show episodic fluctuations in plasma LH, which are not correlated with changes in FSH levels (Katongole, Naftolin & Short, 1974;Lee et al., 1976a). This difference between ewes and rams is also evident in the response to LH-RH; the mature ram shows an increase in plasma LH but very little or no increase in plasma FSH concentrations (Hopkinson, Pant & Fitzpatrick, 1974;Lee et al., 1976b).Following observations on the effect of oestrogen on plasma LH concentrations in freemartin sheep and heifers (Short, 1974;Saba, Symons, Cunningham & Boarer, 1976) which suggested that responses could be of the male or female type, it was of interest to determine the pattern of plasma hormone levels in freemartin sheep. This paper presents data on some plasma hormones in a mas¬ culinized freemartin ewe, its male sibling, three normal rams, and four wethers. MethodsAll the sheep used were Dorset Horns; the three rams, freemartin ewe and its male sibling were 12 months and the wethers 18 months old when the studies were conducted. The freemartin and its male sibling were the surviving pair of triplets : at birth fetal distribution was found to be freemartin and dead male in the left uterine horn and live male sibling in the right horn. The freemartin had palpable testes in the inguinal region, displayed aggressive male behaviour and had 60% XY cells in the blood. The male sibling was apparently normal. The sheep were housed indoors and jugular vein samples were taken every 2 h for 24 h from the rams, freemartin and male sibling (in March), and at 1-h intervals for 8 h from the wethers (in May).Plasma FSH was determined by the solid-phase assay as described by Cunningham & Hebert (1973). Plasma LH was assayed by a solid-phase method utilizing PVC haemagglutination trays coated with antiserum (Boarer, Morris & Mackintosh, 1977): the intra-assay variation was 9-6% and the sensitivity was 0-5-1 ng LH/ml plasma. All plasma samples were run in the same assay. FSH and LH concentrations are expressed as ng of NIH-FSH-S4 and NIH-LH-S17 respectively/ml. Plasma samples (100-500 µ ) were extracted with 5 ml light petroleum ether (b. pt. 40-60°C) for progesterone determinations or 5 ml diethyl ether for testosterone, androstenedione and free oestrogens, and the steroids in the extracts were assayed by the charcoal-gelatin disk method (Saba, 1976). Results and discussionWethers. The plasma concentrations of LH and FSH fluctuated irregularly during the 8-h observation period, but there was n...

“…No other investigations of positive feedback responses of ovine freemartins were found, although some studies have been undertaken in cattle that support the results of the present experiments. For example, Saba et al (1976) reported that only one of 19 freemartins underwent an LH surge after administration of 500 µg oestradiol, although a higher dose (1.0 mg) was more effective (Cunningham et al, 1977). In the present study, ovine freemartins received either 50 or 1000 µg oestradiol per day, so it appears that they are, if anything, even less sensitive to its positive feedback effects than their bovine counterparts.…”

Section: Discussionmentioning

confidence: 48%

Inter-relationships among gonadotrophins, reproductive steroids and inhibin in freemartin ewes

Tj¹,

Kc²,

Se³

et al. 2001

Freemartins are sterile XX/XY chimaeras that occur as a result of placental fusion between male and female fetuses during early pregnancy. Freemartins occur predominantly in cattle, although the prevalence of ovine freemartinism is increasing. In this study, the reproductive endocrinology of ovine freemartins was compared with that of normal sheep. Freemartins had significantly (P < 0.001) higher basal concentrations of LH and FSH than did normal ewes or rams, although the response of LH to GnRH (10 microg) was similar in freemartins, ewes and rams. Resting concentrations of oestradiol were similar in freemartins and ewes and were increased in both after eCG administration. Testosterone concentrations were higher in freemartins than in ewes, but were unresponsive to GnRH or eCG. Administration of 62.5 mg progesterone or 25 lg oestradiol twice a day for 3 days suppressed LH concentrations to baseline values in freemartins, ewes and rams. In ewes, 500 microg oestradiol administered twice a day caused preovulatory surges in LH concentrations, but suppressed LH in freemartins to baseline values. Thus, LH secretion can potentially be regulated in freemartins by gonadal steroids. FSH concentrations in freemartins were not suppressed by doses of inhibin that were effective in ewes and rams. Therefore, freemartins behave in part like castrated animals, as they have high basal concentrations of LH and FSH, which can be stimulated by GnRH and suppressed by gonadal steroids. Conversely, inhibin does not suppress FSH concentrations in freemartins, and freemartins have circulating concentrations of steroids intermediate between those of castrated and normal animals.