Tadao Okamura

Presence of pituitary adenylate cyclase-activating polypeptide (PACAP) and its relaxant activity in the rectum of a teleost, the stargazer, Uranoscopus japonicus

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide and a member of the secretin/glucagon superfamily of peptides that include vasoactive intestinal polypeptide. PACAP is not only present in the central nervous system but also in peripheral organs, such as the gastrointestinal tract, gonads and adrenal glands, and plays various roles in mammals. Recently, we isolated and characterized PACAP, which is very similar to PACAP of mammalian origin, from the brain of a teleost, the stargazer, Uranoscopus japonicus. In the present study, the expression of PACAP mRNA was detected in the stargazer rectum using the reverse transcriptase/polymerase chain reaction (RT-PCR) method. The distribution of PACAP-like immunoreactivity in the rectum was also examined immunohistochemically, using an antiserum raised against PACAP 27, and PACAP-like immunoreactive neuronal cell bodies and fibers were found in the myenteric plexuses and the smooth muscle layers of the rectum. The present study also investigated the relaxant activity of synthesized homologous PACAP on rectal contraction. Stargazer PACAP, like that of mammalian origin, inhibited contractions stimulated by acetylcholine or potassium chloride. PACAP-induced inhibition was not affected by preincubation with atropine, propranolol, or phentolamine. These results suggest that PACAP may act directly as an inhibitory neuropeptide in the stargazer rectum.

Mesenteric Lymph Flow in Endotoxemic Guinea Pigs

BACKGROUND Lipopolysaccharide (LPS) is a structural component of the outer membrane of gram-negative bacteria. LPS activates the host cells, leading to the production and release of proinflammatory cytokines. Given the induction duration for the release of cytokines, the initial mechanisms that produce LPS action on a timescale of minutes are not fully understood. We studied the effect of initial LPS-induced action on the lymphatic system by measuring the time-dependent changes in mesenteric lymph flow in guinea pigs in vivo. In addition, we determined the leakage of plasma protein into the lymphatic system using Evans blue dye. METHODS AND RESULTS The mesenteric lymphatic vessel was cannulated with a polyethylene catheter. We administered drugs via a catheter in jugular vein. The control animals received vehicle intravenously (i.v.). The experimental group received 1 mg/kg or 10 mg/kg LPS i.v. Twenty minutes before injection of the vehicle or LPS, Evans blue dye (5 mg/kg i.v.) was administered. Lymph output was measured every 20 min. The amount of Evans blue in the lymph was determined by spectrophotometry. The mesenteric lymph showed a steady flow rate of approximately 290 μL/kg/20 min. The lymph flow immediately increased after the administration of LPS and reached 3.4-fold and 7.4-fold after 1 h of 1 mg/kg and 10 mg/kg LPS injection, respectively. The albumin content in lymph significantly increased in proportion to the increased lymph volume. CONCLUSIONS These results suggest that the early increase in mesenteric lymph flow rate in guinea pigs produced by LPS is mediated by vascular hyperpermeability and plasma albumin leakage.