The Obestatin/Ghrelin System as a Novel Regulatory Mechanism of Iris Muscle Contraction

Abstract

The objective of this study was the assessment of heart-rate (HR) dynamics with linear and nonlinear methods during episodes of mechanical ventilation and acute anoxia in rats. Namely, to assess whether linear and nonlinear HR analysis was able to discriminate acute anoxia from baseline in rats and if this was consistent with human foetal and adult studies. Five HR segments of 1 min duration, during baseline recording, mechanical ventilation and first, second and third minutes of induced acute anoxia, were analysed in ten adult Wistar rats. Linear time and frequency domain and nonlinear methods were used, namely mean HR (mHR), long-term irregularity (LTI), interval index (II), low frequency (LF) and high frequency (HF), approximate entropy (ApEn) and sample entropy (SampEn). New parameters for the entropy indices are proposed for the analysis of rats' HR. Bootstrap percentile confidence intervals and nonparametric statistical tests were used in the evaluation of the differences between segments. During mechanical ventilation a clear spectral band was detectable at the ventilation rate, but mHR, II and the 'new' entropy indices were the only significantly changed indices. In the transition from baseline-mechanical-ventilation to mechanical-ventilationinduced anoxia, a statistically significant decrease of mHR, II and entropy indices was observed, clearly discriminating these two instances, whereas most linear indices increased. With continued anoxia, most linear indices decreased significantly, whereas entropy remained stably low. These results are consistent with other foetal human and non-human studies and evidence that the rat model may be used for further research on linear and nonlinear analysis of heart-rate dynamics. The transition from baseline to acute anoxia was encompassed by signs of increased activation of the autonomic nervous system sympathetic branch, and decreased or blunted activity of the HR complexity regulatory centres.

Ghrelin Attenuates Retinal Neuronal Autophagy and Apoptosis in an Experimental Rat Glaucoma Model

“…40 Ghrelin may also relax both the iris sphincter and dilator muscles in eyes. 17,41 However, in the present study, intraper- itoneal injection of ghrelin did not significantly change the elevated IOP in COH eyes, and a recent study has reported that after the IOP is increased, intraperitoneal treatment of ghrelin every day for 14 days does not significantly change the IOP in a rat experimental glaucoma model. 22 We speculate that different delivery methods and/or delivery times, such as before or after the IOP elevation, may have influenced the effect of ghrelin on the IOP in COH eyes.…”

Plasma and aqueous humour levels of ghrelin in open‐angle glaucoma patients

“…3 Concerning its functional significance, there is initial evidence for a role of ghrelin in iris muscle dynamics. 3,22 Its effects seem to be mediated by the GHSR-1a for the dilator and a different receptor for the sphincter muscle in animal studies. 3 However, there are no data available on its role in iris muscle kinetics in human eyes.…”

Lack of direct effects of acyl ghrelin, des-acyl ghrelin, and obestatin on rat lower esophageal sphincter motility in vitro

“…34 In addition, an acyl ghrelin fragment (human ghrelin 1À5 ) decreased basal tension, electric field stimulationelicited contractions and tension of the carbachol-induced contraction of the iris sphincter, whereas obestatin decreased the basal tension and increased the carbachol-induced contraction of the iris sphincter in rabbits. 35 Thus, investigating the effects of ghrelin gene-derived peptides in the LES is very interesting.…”