Cellular in vivo imaging reveals coordinated regulation of pituitary microcirculation and GH cell network function

Abstract

Growth hormone (GH) exerts its actions via coordinated pulsatile secretion from a GH cell network into the bloodstream. Practically nothing is known about how the network receives its inputs in vivo and releases hormones into pituitary capillaries to shape GH pulses. Here we have developed in vivo approaches to measure local blood flow, oxygen partial pressure, and cell activity at single-cell resolution in mouse pituitary glands in situ. When secretagogue (GHRH) distribution was modeled with fluorescent markers injected into either the bloodstream or the nearby intercapillary space, a restricted distribution gradient evolved within the pituitary parenchyma. Injection of GHRH led to stimulation of both GH cell network activities and GH secretion, which was temporally associated with increases in blood flow rates and oxygen supply by capillaries, as well as oxygen consumption. Moreover, we observed a time-limiting step for hormone output at the perivascular level; macromolecules injected into the extracellular parenchyma moved rapidly to the perivascular space, but were then cleared more slowly in a size-dependent manner into capillary blood. Our findings suggest that GH pulse generation is not simply a GH cell network response, but is shaped by a tissue microenvironment context involving a functional association between the GH cell network activity and fluid microcirculation.blood flow | hormone pulsatility | oxygen pressure | tissue microenvironment | extracellular space

Pituitary growth hormone network responses are sexually dimorphic and regulated by gonadal steroids in adulthood

“…S3, Upper) exhibited GH cell clusters interlinked with cell strands. As reported previously (12,16), GH cell clustering, as reflected in the volume/surface ratio of the GH cell network, increased transiently at puberty in males. We were not able to show a similar increase in females during sexual maturation (Fig.…”

Rapid sensing of circulating ghrelin by hypothalamic appetite-modifying neurons

“…To access deep structures on the ventral surface of the brain and directly visualize vessels of the ME in vivo, surgical approaches developed for functional imaging of the pituitary (14) were combined with a multiphoton microscope adapted with longworking distance (2 cm) objectives (Fig. 1A).…”

“…All animal studies complied with the animal welfare guidelines of the European Community and were approved by the Direction of Veterinary Departments of Hérault and Nord, France (59-350134), and the Languedoc Roussillon Institutional Animal Care and Use Committees (CE-LR-0818). The ME was exposed using a surgery approach previously described for in vivo studies of the pituitary gland (14).…”

“…To evaluate the role of fenestrated ME/ARH capillaries in rapid detection of peripheral signals by the hypothalamus, we used a recently developed in vivo imaging approach to visualize in real time the extravasation of fluorescent molecules (14). Ghrelin was chosen as a candidate hormone because its acute effects upon feeding behavior (15), together with a short circulating half-life, demand the presence of rapid and precise sensing mechanisms.…”

Curcumin suppresses HIF1A synthesis and VEGFA release in pituitary adenomas

“…However, VEGFA also has other physiological functions such as maintaining the existing blood vessel system and regulating the vessel permeability by stimulating capillary fenestration (Ferrara 2004). An extremely dense intrapituitary vascular system (Viacava et al 2003) and highly permeable capillary endothelial cells are essential for the rapid regulation and release of hormones within the anterior pituitary (Lafont et al 2010). Therefore, VEGFA is already produced under normoxic conditions in the normal pituitary by FS cells, which are considered to be the major source of this factor in the adenohypophysis (Gospodarowicz et al 1989, Gloddek et al 1999.…”