In vivo imaging reveals an essential role of vasoconstriction in rupture of the ovarian follicle at ovulation.

Rupture of the ovarian follicle releases the oocyte at ovulation, a timed event that is critical for fertilization. It is not understood how the protease activity required for rupture is directed with precise timing and localization to the outer surface, or apex, of the follicle. We hypothesized that vasoconstriction at the apex is essential for rupture. The diameter and blood flow of individual vessels and the thickness of the apical follicle wall were examined over time to expected ovulation using intravital multiphoton microscopy. Vasoconstriction of apical vessels occurred within hours preceding follicle rupture in wild-type mice, but vasoconstriction and rupture were absent in Amhr2(cre/+)SmoM2 mice in which follicle vessels lack the normal association with vascular smooth muscle. Vasoconstriction is not simply a response to reduced thickness of the follicle wall; vasoconstriction persisted in wild-type mice when thinning of the follicle wall was prevented by infusion of protease inhibitors into the ovarian bursa. Ovulation was inhibited by preventing the periovulatory rise in the expression of the vasoconstrictor endothelin 2 by follicle cells of wild-type mice. In these mice, infusion of vasoconstrictors (either endothelin 2 or angiotensin 2) into the bursa restored the vasoconstriction of apical vessels and ovulation. Additionally, infusion of endothelin receptor antagonists into the bursa of wild-type mice prevented vasoconstriction and follicle rupture. Processing tissue to allow imaging at increased depth through the follicle and transabdominal ultrasonography in vivo showed that decreased blood flow is restricted to the apex. These results demonstrate that vasoconstriction at the apex of the follicle is essential for ovulation.

Endothelin-2 deficiency causes growth retardation, hypothermia, and emphysema in mice.

To explore the physiological functions of endothelin-2 (ET-2), we generated gene-targeted mouse models. Global Et2 knockout mice exhibited severe growth retardation and juvenile lethality. Despite normal milk intake, they suffered from internal starvation characterized by hypoglycemia, ketonemia, and increased levels of starvation-induced genes. Although ET-2 is abundantly expressed in the gastrointestinal tract, the intestine was morphologically and functionally normal. Moreover, intestinal epithelium-specific Et2 knockout mice showed no abnormalities in growth and survival. Global Et2 knockout mice were also profoundly hypothermic. Housing Et2 knockout mice in a warm environment significantly extended their median lifespan. However, neuron-specific Et2 knockout mice displayed a normal core body temperature. Low levels of Et2 mRNA were also detected in the lung, with transient increases soon after birth. The lungs of Et2 knockout mice showed emphysematous structural changes with an increase in total lung capacity, resulting in chronic hypoxemia, hypercapnia, and increased erythropoietin synthesis. Finally, systemically inducible ET-2 deficiency in neonatal and adult mice fully reproduced the phenotype previously observed in global Et2 knockout mice. Together, these findings reveal that ET-2 is critical for the growth and survival of postnatal mice and plays important roles in energy homeostasis, thermoregulation, and the maintenance of lung morphology and function.

Characterisation of a rat model of pulmonary arterial hypertension.

INTRODUCTION: Pulmonary hypertension portends an adverse outcome. Animal models have improved current understanding of the complex pathophysiology of the disease, but may be technically demanding. Moreover, plexiform vascular lesions are rarely observed, limiting the extrapolation to human pathophysiology. The aim of the present study was first, to assess the feasibility of closed-chest pressure recordings, and mainly, to further characterise a new model of endothelin receptor-B deficient rats. METHODS: Jugular venous catheterisation was assessed in 15 Wistar rats. Pressure recordings via a left lateral thoracotomy and histological findings were compared in three rat groups (age 20 +/- 1 weeks, weight 200-250 g): (a) wild type (n = 10, group A); (b) wild type after monocrotaline injection (n=10, group B); and (c) endothelin receptor-B deficient rats (n = 10, group C) after monocrotaline injection. RESULTS: Pressure recordings via the jugular approach were feasible in only 3 (20%) rats. Compared to group A, there was a trend (H = 4.6, p = 0.0962) towards increased mortality in groups B and C, due to respiratory arrest during intubation attempts. Pulmonary artery systolic pressure in group C was 24.7 +/- 1.3 mmHg, higher than in group B (21.5 +/- 1.2, p = 0.036) or group A (11.8 +/- 0.5, p < 0.0001). Adverse pulmonary vascular remodelling was more prominent in group C than in group B. CONCLUSIONS: Endothelin receptor-B deficient rats constitute a useful model of pulmonary artery hypertension after monocrotaline injection. The ease of pressure recordings via a left lateral thoracotomy may aid in the more widespread use of this model.