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PubMed1998

Components of the neuronal exocytotic machinery in the anterior pituitary of the ovariectomised ewe and the effects of oestrogen in gonadotropes as studied with confocal microscopy.

We have investigated exocytotic proteins in ovine pituitary cells and sought to identify changes in expression of these proteins related to the effects of estrogen on luteinising hormone (LH) secretion in the ovariectomised ewe. Sheep were treated with either oestradiol benzoate, or oil (i.m.) and blood samples collected for LH assay. Pituitaries were perfusion-fixed and dual-label immunohistochemistry was performed to identify hormone-secreting cells, and colocalise synaptic proteins within different cell types. Synaptophysin, SNAP-25, VAMP-2, rab3A, Munc-18-1, alpha/beta-SNAP, csp, and secretogranin II were detected in gonadotropes and somatotropes. Lactotropes were positive for SNAP-25 and synaptophysin (other synaptic proteins not investigated). Synaptotagmin I was detected in gonadotropes and lactotropes, but not somatotropes. Synaptophysin, SNAP-25, synaptotagmins I, II and III, VAMP-2, rab3A, Munc-18-1, alpha/beta-SNAP, csp, and secretogranin II were detected in nerve fibres of the posterior lobe. Membrane staining for SNAP-25 and weak cytoplasmic labelling for both synaptotagmin I and secretogranin II were detected in the intermediate lobe. Syntaxin and complexin II antibodies did not label any region of the ovine pituitary. Oestrogen treatment, to induce a pre-ovulatory-like LH surge, caused migration of LH-containing secretory granules toward the plasma membrane of gonadotropes, but did not alter the percentage of gonadotropes expressing each exocytotic protein. Oestrogen treatment caused a similar redistribution of csp and secretogranin II staining in gonadotropes. We conclude that synaptic protein expression is not altered in the anterior pituitary at the time when LH secretion is maximal. The ubiquitous distribution of many exocytotic proteins suggests that all hormone-secreting cells of the pituitary gland contain the same, or similar exocytotic machinery, but distinct 'activating factors' are required to selectively trigger the secretion of individual hormones.

Animals↗
PubMed2004

Arterial permeability and efflux of apolipoprotein B-containing lipoproteins assessed by in situ perfusion and three-dimensional quantitative confocal microscopy.

OBJECTIVES: There is accumulating evidence that an increased risk of cardiovascular disease (CVD) is not simply caused by the degree of arterial exposure to plasma lipoproteins but, in addition, is determined by the affinity of the vasculature for different lipoprotein phenotypes. In this study we compare the delivery and efflux of 2 atherogenic lipoproteins to further understand the factors that regulate cholesterol accumulation in early atherogenesis. METHODS AND RESULTS: Lipoproteins containing apolipoprotein (apo) B100 (a low-density lipoprotein [LDL]) and apoB48 (chylomicron remnants) were isolated and differentially conjugated with fluorophores and simultaneously perfused at equivalent concentrations in situ through rabbit carotid vessels. Perfusion systems were established to quantify and differentiate between lipoprotein arterial delivery and efflux. The total average rate of delivery for LDL particles (23 nm) compared with chylomicron remnants (50 nm) was 4427 particles/min(-1) per microm3 and 452 particles/min(-1) per microm3, respectively. In contrast, the average rate of efflux was 3195 particles/min(-1) per microm3 and 163 particles/min(-1) per microm3 for LDL and chylomicron remnants, respectively. CONCLUSIONS: Results indicate that although LDL particles have a higher rate of delivery, they efflux more readily from arterial tissue compared with the larger chylomicron remnants. Collectively, our findings highlight that lipoproteins permeate through arterial tissue differently and may be dependent on the phenotype and potential interactions with extracellular matrix components.

Animals↗