Characterization of the Mel1c melatoninergic receptor in platypus (Ornithorhynchus anatinus)

Melatonin is a neurohormone produced in both animals and plants. It binds at least three G-protein-coupled receptors: MT1 and MT2, and Mel1cGPR. Mammalian GPR50 evolved from the reptilian/avian Mel1c and lost its capacity to bind melatonin in all the therian mammal species that have been tested. In order to determine if binding is lost in the oldest surviving mammalian lineage of monotremes we investigated whether the melatonin receptor has the ability to bind melatonin in the platypus (Ornithorhynchus anatinus), and evaluated its pharmacological profile. Sequence and phylogenetic analysis showed that platypus has in fact retained the ancestral Mel1c and has the capacity to bind melatonin similar to other mammalian melatonin receptors (MT1 and MT2), with an affinity in the 1 nM range. We also investigated the binding of a set of melatoninergic ligands used previously to characterize the molecular pharmacology of the melatonin receptors from sheep, rats, mice, and humans and found that the general profiles of these compounds make Mel1c resemble human MT1 more than MT2. This work shows that the loss of GPR50 binding evolved after the divergence of monotremes less than 190MYA in therian mammals.

Effect of epinephrine on pancreatic beta-cell and alpha-cell function in patients with NIDDM

The purposes of this study were to determine whether patients with non-insulin-dependent diabetes mellitus (NIDDM) have an enhanced glycemic response to epinephrine (EPI) and to quantitate the effect of physiological elevations of EPI on pancreatic islet function in these patients. The increment of plasma glucose (PG) in response to 45 min of EPI infusion (mean plasma EPI 2490 pM) was more than twofold greater in nine NIDDM patients than in 20 nondiabetic control subjects (mean +/- SE delta PG 3.9 +/- 0.3 vs. 1.7 +/- 0.1 mM, P less than 0.0001). The effects of EPI on beta-cell and alpha-cell function were compared in nine NIDDM patients and 9 age- and weight-matched control subjects during infusions of saline or two doses of EPI on separate days (mean plasma EPI 270, 1120, and 2490 pM). On each day, the acute insulin response (AIR) and acute glucagon response (AGR) to 5 g i.v. arginine were measured at three matched steady-state PG levels (means of 9, 14, and 29 mM). Beta-Cell sensitivity to glucose (slope of glucose potentiation) and beta-cell secretory capacity, or AIRmax (AIR at the highest clamped PG level), were calculated. In control subjects, EPI inhibited the AIR at PG concentrations of 9 and 14 mM (both P less than 0.05) but had no effect on the AIRmax, resulting in a rightward shift of the curve relating the AIR and PG and a decrease in the slope of glucose potentiation (P less than 0.01). In contrast in NIDDM patients, EPI inhibited the AIR at all PG levels, including the AIRmax (all P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-adrenergic blockade decreases norepinephrine release in humans

Beta-Adrenergic blockade with propranolol (PRP) has been reported to cause an increase in plasma norepinephrine (NE) levels in humans, which suggests that a reflex increase in sympathetic nervous system (SNS) vasoconstrictor tone compensates for the hypotensive effect of beta-adrenergic blockade. However, plasma NE levels are an indirect measure of SNS activity. We have developed a two-compartment model of NE kinetics to estimate NE release into an extravascular compartment as a more comprehensive measure of systemic SNS activity. To determine whether beta-adrenergic blockade alters extravascular NE release, we studied nine healthy subjects during sequential infusions of saline and PRP. During PRP infusion, there was an increase in plasma NE levels [1.03 +/- 0.13 to 1.27 +/- 0.21 (SE) nM; P = 0.05], but the extravascular NE release rate decreased significantly (15.5 +/- 1.6 to 9.2 +/- 1.2 nmol.min-1.m-2, P = 0.0002). The plasma NE concentration increased despite the fall in extravascular NE release rate primarily because the clearance of NE from plasma declined (1.55 +/- 0.08 to 1.18 +/- 0.07 l.min-1.m-2, P = 0.0001); the NE spillover rate into plasma did not change (1.73 +/- 0.18 to 1.75 +/- 0.23 nmol.min-1.m-2, P = 0.89). We conclude that PRP decreases extravascular NE release in humans. Suppression of SNS activity may be an additional mechanism of action of nonselective beta-adrenergic antagonists in humans.

Hyperphoretic Dispersal of a Pyxidiophora Anamorph

It has been suggested that Thaxteriola species and other minute, nonmycelial fungi associated with arthropods have phylogenetic relationships with the Laboulbeniales. However, direct development of the thallus of Thaxteriola from an ascospore of Pyxidiophora has now been discovered. Thaxteriola is specialized for dispersal by mites carried on pine bark beetles; other fungi dispersed by arthropods in this symbiotic assemblage rely primarily on arthropod specializations.