Is the canine corpus luteum an insulin-sensitive tissue?

This study aimed to determine in the canine corpus luteum throughout the dioestrus (1) the influence of insulin on glucose uptake; (2) the regulation of genes potentially involved; and (3) the influence of hypoxia on glucose transporter expression and steroidogenesis, after treatment with cobalt chloride (CoCl2). Glucose uptake by luteal cells increased 2.7 folds (P < 0.05) in response to insulin; a phenomenon related to increased expression of glucose transporter (GLUT) 4 and phosphorylation of protein kinase B (AKT). The gene expression of insulin receptor and SLC2A4 (codifier of GLUT4) genes after insulin stimulation increased on day 20 post ovulation (p.o.) and declined on day 40 p.o. (P < 0.05). Regarding potentially involved molecular mechanisms, the nuclear factor kappa B gene RELA was upregulated on days 30/40 p.o., when SLC2A4 mRNA was low, and the interleukin 6 (IL6) gene was upregulated in the first half of dioestrus, when SLC2A4 mRNA was high. CoCl2 in luteal cell cultures increased the hypoxia-inducible factor HIF1A/HIF1A and the SLC2A4/GLUT4 expression, and decreased progesterone (P4) production and hydroxyl-delta-5-steroid dehydrogenase 3 beta (HSD3B) mRNA expression (P < 0.05). This study shows that the canine luteal cells are responsive to insulin, which stimulates glucose uptake in AKT/GLUT4-mediated pathway; that may be related to local activity of RELA and IL6. Besides, the study reveals that luteal cells under hypoxia activate HIF1A-modulating luteal function and insulin-stimulated glucose uptake. These data indicate that insulin regulates luteal cells' glucose disposal, participating in the maintenance and functionality of the corpus luteum.

Morphological features and vascularization study of caprine cyclic corpus luteum / Características morfológicas e estudo da vascularização do corpo lúteo cíclico de cabras ao longo do ciclo estral

Corpus luteum is a temporary endocrine gland that regulates either the estrous cycle and pregnancy. It presents extreme dependency on the adequate blood supply. This work aims to evaluate goat corpus luteum (CL) vascular density (VD) over the estrous cycle. For that purpose, 20 females were submitted to estrus synchronization/ovulation treatment using a medroxyprogesterone intra-vaginal sponge as well as intramuscular (IM) application of cloprostenol and equine chorionic gonadotrophine (eCG). After sponge removal, estrus was identified at about 72hs. Once treatment was over, female goats were then subdivided into 4 groups (n=5 each) and slaughtered on days 2, 12, 16 and 22 after ovulation (p.o). Ovaries were collected, withdrawn and weighted. CL and ovaries had size and area recorded. Blood samples were collected and the plasma progesterone (P4) was measured through RIA commercial kits. The VD was 24.42±6.66, 36.26±5.61, 8.59±2.2 and 3.97±1.12 vessels/mm² for days 2, 12, 16 and 22 p.o, respectively. Progesterone plasma concentrations were 0.49±0.08, 2.63±0.66, 0.61±0.14 and 0.22±0.04ng/ml for days 2, 12, 16 e 22 p.o, respectively. Studied parameters were affected by the estrous cycle phase. Values greater than 12 p.o were observed. In the present work we observed that ovulation occurred predominantly in the right ovary (70 percent of the animals), which in turn presented bigger measures than the contra lateral one. There is a meaningful relationship between the weight and size of the ovary and these of CL (r=0.87, r=0.70, respectively, p<0.05). It is possible to conclude that morphology of goat's ovaries and plasma progesterone concentration changed according to estrous cycle stages. We propose these parameters can be used as indicators of CL functional activity.

O corpo lúteo é uma glândula endócrina temporária que regula tanto o ciclo estral quanto a prenhez, apresentando extrema dependência de aporte sanguíneo adequado. Objetivaram-se avaliar mudanças morfométricas dos ovários e densidade vascular (DV) dos corpos lúteos (CL) de cabras ao longo do ciclo estral (AOLC). Vinte animais foram submetidos ao tratamento para indução/sincronização do estro, usando esponjas intravaginais commedroxiprogesterona, associadas a aplicações intramusculares de cloprostenol e gonadotrofina coriônica eqüina. Após remoção das esponjas, o estro foi identificado em aproximadamente de 72h. Concluído o tratamento, as cabras foram subdivididas em 4 grupos (n=5 cada) para abate nos dias 2, 12, 16 e 22 após ovulação (p.o.). Posteriormente, foram retirados os ovários e realizadas as mensurações de peso, tamanho e área do órgão e dos CL. Amostras de sangue foram coletadas e a progesterona sérica (P4) mensurada utilizando-se RIA convencional. A DV média dos CL AOLC foi 24,42±6,66; 36,26±5,61; 8,59±2,2 e 3,97±1,12 vasos/mm2 para os dias 2, 12, 16 e 22 p.o., respectivamente. A concentração média de P4 foi de 0,49±0,08; 2,63±0,66; 0,61±0,14 e 0,22±0,04ng/ml para os dias 2, 12, 16 e 22 p.o., respectivamente. Os parâmetros em estudo também se mostraram afetados pela fase do ciclo estral, sendo observados os maiores (p < 0,05) valores no dia 12 p.o. Neste experimento, a ovulação ocorreu predominantemente no ovário direito (70 por cento dos animais), o qual apresentou medidas maiores que o contralateral. Observou-se ainda alta correlação significativa entre o peso do ovário e o do CL (r=0,87; p<0,05) e entre o tamanho destes órgãos (r=0,70; p<0,05). Conclui-se que, a morfologia dos ovários de cabras e a concentração sérica de progesterona variam em função da fase do ciclo estral e podem ser utilizadas como parâmetro na avaliação funcional do órgão.