Compensation by pulsatile GnRH infusions for incompetence for oestradiol-induced LH surges in long-term ovariectomized gilts and castrated male pigs.

The aim of this study was to investigate incompetence for oestradiol-induced LH surges in long-term ovariectomized gilts and male pigs. Gilts (250 days old; n = 36), which had been ovariectomized 30 (OVX 30) or 100 days (OVX 100) before the start of treatment, were challenged i.m. with oestradiol benzoate and were either given no further treatment, fed methallibure to inhibit endogenous GnRH release or fed methallibure and given i.v. pulses of 100 or 200 ng GnRH agonist at 1 h intervals during the LH surge (48-96 h after oestradiol benzoate). The same treatments were applied to long-term orchidectomized male pigs (ORC, n = 23). In addition, one ORC group was not injected with oestradiol benzoate but was fed methallibure and given pulses of 200 ng GnRH agonist. Oestradiol benzoate alone induced an LH surge in the OVX 30 group only (5/6 gilts), methallibure suppressed (P < 0.05) oestradiol benzoate-induced LH secretion, while pulses of 100 ng GnRH agonist in animals fed methallibure produced LH surges in four of six OVX 30 and four of six OVX 100 gilts. The induced LH surges were similar to those produced by oestradiol benzoate alone in OVX 30 gilts. Pulses of 200 ng GnRH agonist produced LH surges in OVX 30 (6/6) and OVX 100 (6/6) gilts and increased the magnitude of the induced LH surge in OVX 100 gilts (P < 0.05 compared with 100 ng GnRH agonist or OVX 30 control). Pulses of 200 ng GnRH agonist also induced LH surge release in ORC male pigs (5/6), but were unable to increase LH concentrations in a surge-like manner in ORC animals that had not been given oestradiol benzoate, indicating that oestradiol increases pituitary responsiveness to GnRH. These results support the hypothesis that oestradiol must inhibit secretion of LH before an LH surge can occur. It is concluded that incompetence for oestradiol-induced LH surges in long-term ovarian secretion-deprived gilts and in male pigs is due to the failure of oestradiol to promote a sufficient increase in the release of GnRH.

[Conclusions on the use of Suisychron in the USSR]. / Istogi primeneniia suisinkhrona v SSSR.

Suisynchron was applied to 2,258 gilts, including 850 from breeding farms. Forty-four pigs were checked to elucidate the influence of sexual maturity on the success of oestrus synchronisation. Suisynchron-Prämix was fed to the animals over 20 days, the daily dose for each pig having been 5 g. Twenty-four hours were allowed to elapse from the last administration before 1,500 I.U. PMSG were injected. Synchronised oestrus occurred in 81.2 per cent of all pigs between four and six days from serum injection. Fertilisation in response to first insemination was recorded from 72.9 percent of the pigs, their fertility rate being 9.7 piglets from each farrowing sow. The results of oestrus synchronisation obtained from fattening pigs were somewhat inferior to those recorded from pigs of breeding units. Suisynchron and serum of pregnant mares can synchronise oestrus in 91 per cent of all mateable sows with no previous cycle. The fertility rates recorded from such pigs did not exceed 59 per cent or were between 28.9 and 31.9 per cent lower than those recordable from pigs with a cycle history prior to the use of Suisynchron.

[Studies of the high toxicity of zinc-metallibur]. / Izuchenie ostroi toksichnosti tsink-metallibura.

The high toxicity of Zine-Metallibur was tested in gilts aged eight months and weighing between 78 and 96 kg. Zinc-Metallibur, either 1 g/kg live weight or a quantity 1,000 times that used for synchronisation, was admixed to feed rations and introduced directly into the stomach through and intra-oesophageal tube. Fodder with the entire dose admixed is rejected by the pig. Direct intragastric administration of the same amount, however, is possible and does not cause death.

A possible role for oxytocin in sperm transport in the male rabbit.

Administration of methallibure (50 mg/kg body weight, daily) to male rabbits resulted in a 45% reduction in sperm number in ejaculates obtained during the treatment period. Recovery occurred within 48 h after the last dose of methallibure. This decrease in sperm number did not occur when oxytocin (0-2 i.u./kg body weight) was administered simultaneously with methallibure. This suggests that methallibure prevents the release of oxytocin during ejaculation.

[Pharmacologic-endocrinological findings in animal experiments with TURISYNCHRON and SUISYNCHROM. 2. Toxicologic findings]. / Pharmakologisch-endokrinologische Befunde bei der Prüfung von TURISYNCHRON) und SUISYNCHRON) im Tierexperiment. 2. Mitteilung: Toxikologische Befunde

Acute, subacute and chronic toxicity of TURISYNCHRON and its zinc complex (SUISYNCHRON) was tested in mice, rats and dogs. The acute toxicity of SUISYNCHRON was lower than that of TURISYNCHRON in mice and rats. Ulcerative lesions in the duodenum produced by high doses of SUISYNCHRON were quantitatively less pronounced than those produced by similar doses of TURISYNCHRON. Subacute toxicity testing in rats showed that neither preparation had any toxic effect on haematological, clinical chemical or histological criteria in the dosages selected. Chronic toxicity testing of TURISYNCHRON in dogs did not reveal any evidence of toxic damage.