GHRL and obesity due to melanocortin 4 receptor deficiency: Perry et al. went on to demonstrate that when acetate is infused in physiological amounts, to match endogenous rates of acetate turnover in HFF obese rats, this perturbation led to activation of the parasympathetic nervous system, which in turn promoted increased glucose-stimulated insulin secretion (GSIS), increased ghrelin secretion, hyperphagia and obesity [3].