Search Results

Summary. The effect of insulin-like growth factors (IGFs) and insulin on the release of progesterone and oxytocin from bovine corpus luteum was investigated at early (days 5–7), mid- (days 8–12) and late (days 15–18) luteal phases of the oestrous cycle in an in vitro microdialysis system. The expression of specific receptors was evaluated in bovine corpora lutea of the respective luteal stages.

A 30 min infusion of IGF-1, IGF-2 (1·3, 13 and 130 nmol l⁻¹) or insulin (13, 130 and 1300 nmol l⁻¹) caused a stimulation of the release of progesterone (P < 0·05). IGF-1 was most effective in releasing progesterone. Oxytocin release from corpora lutea was stimulated by insulin at all doses tested (13-1300 nmol l⁻¹), whereas the IGFs were only effective at the highest dose (130 nmol l⁻¹) applied. The high doses of IGFs (130 nmol l⁻¹) and insulin (1300 nmol l⁻¹) stimulated the release of progesterone and oxytocin throughout the luteal phase (P < 0·05). For all three peptides, greatest stimulation was seen during the late luteal phase (days 15-18 of the oestrous cycle) with the peak of progesterone release directly related to peptide infusion (P < 0·05). In addition, IGF-1 stimulated total release of progesterone (units in 4 h) after the beginning of the stimulation during this phase (P < 0·05). IGF-1 caused a gradual increase of progesterone even beyond the time of peptide perfusion, whereas IGF-2 and insulin stimulated progesterone release only during the peptide perfusion.

Distinct receptors for IGF-1 and IGF-2 were present in corpora lutea membrane preparations at all stages investigated. Specific binding for insulin was also seen in all stages of the cycle without any cycle-dependent changes in the amount of binding. The displacement of labelled insulin by unlabelled IGF-1 and IGF-2 did not show the rank of order that has been described as typical for insulin receptors (i.e. insulin > IGF-1 > IGF-2), but comparable binding affinities were observed for the three unlabelled ligands. Specific binding of IGF-2 was markedly higher than that of IGF-1 or insulin throughout the cycle (1·9- and 4·9-fold higher compared with IGF-1 and insulin, respectively). Receptor specificity did not change during luteal development. Binding affinity and capacity of IGF-1 receptor was constant throughout the oestrous cycle. Specific IGF-2 binding increased and showed a positive co-operativity towards the end of the cycle. Specific binding of insulin was not significantly different in the three luteal stages examined.

Keywords: corpus luteum; IGFs; insulin; progesterone; oxytocin; cow

The objective of this study was to examine the effect of nutrition during the first 18 weeks of life on the physiological and transcriptional functionality of the hypothalamic (arcuate nucleus region), anterior pituitary and testes in Holstein–Friesian bull calves. Holstein–Friesian bull calves with a mean (±s.d.) age and bodyweight of 19 (±8.2) days and 47.5 (±5.3) kg, respectively, were assigned to either a HIGH (n = 10) or LOW (n = 10) plane of nutrition, to achieve an overall target growth rate of 1.2 or 0.5 kg/day, respectively. At 126 ± 1.1 days of age, all calves were euthanised. Animal performance (weekly) and systemic concentrations of metabolic (monthly) and reproductive hormones (fortnightly) were assessed. Testicular histology, targeted gene and protein expression of the arcuate nucleus region, anterior pituitary and testes were also assessed using qPCR and immunohistochemistry, respectively. The expression of candidate genes in testicular tissue from post pubertal 19-month-old Holstein–Friesian bulls (n = 10) was compared to that of the 18-week-old calves. Metabolite and metabolic hormone profiles generally reflected the improved metabolic status of the calves on the HIGH (P < 0.001). Calves offered a HIGH plane of nutrition were heavier at slaughter (P < 0.001), had larger testes (P < 0.001), larger seminiferous tubule diameter (P < 0.001), more mature spermatogenic cells (P < 0.001) and more Sertoli cells (P < 0.05) in accordance with both morphological and transcriptional data. Overall, testicular gene expression profiles suggested a more mature stage of development in HIGH compared with LOW and were more closely aligned to that of mature bulls. Ghrelin receptor was the only differentially expressed gene between LOW and HIGH calves in either the anterior pituitary (P < 0.05) or arcuate nucleus region of the hypothalamus (P < 0.10) and was upregulated in LOW for both tissues. This study indicates that an enhanced plane of nutrition during early calfhood favourably alters the biochemical regulation of the hypothalamus–anterior pituitary–testicular axis, advancing testicular development and hastening spermatogenesis.

The present study investigated the role of IGF1 in lactating lean and non-lactating obese dairy cows by injecting 1 μg IGF1 into the ovaries prior to superovulation. This amount of IGF1 has been linked with pregnancy loss in women with the polycystic ovary syndrome (PCOS) and was associated with impaired bovine oocyte competence in vitro. Transcript abundance and protein expression of selected genes involved in apoptosis, glucose metabolism, and the IGF system were analyzed. Plasma concentrations of IGF1 and leptin, and IGF1 in uterine luminal fluid (ULF), were also measured. IGF1 treatment decreased embryo viability in lean cows to the levels observed in obese cows. Obese cows were not affected by IGF1 treatment and showed elevated levels of IGF1 (in both plasma and ULF) and leptin. Blastocysts from lean cows treated with IGF1 showed a higher abundance of SLC2A1 and IGFBP3 transcripts. IGF1 treatment reduced protein expression of tumor protein 53 in blastocysts of lean cows, whereas the opposite was observed in obese cows. IGF1 in plasma and ULF was correlated only in the control groups. Blastocyst transcript abundance of IGF1 receptor and IGFBP3 correlated positively with IGF1 concentrations in both plasma and ULF in lean cows. The detrimental microenvironment created by IGF1 injection in lean cows and the lack of effect in obese cows resemble to a certain extent the situation observed in PCOS patients, where IGF1 bioavailability is increased in normal-weight women but reduced in obese women, suggesting that this bovine model could be useful for studying IGF1 involvement in PCOS.