New method for evaluating intestinal contractions in guinea pig by curve fitting

Butyrylated starch increases large bowel butyrate levels and lowers colonic smooth muscle contractility in rats

The short-chain fatty acids acetate, propionate, and butyrate are produced by colonic bacterial fermentation of carbohydrates. Butyrate is important in the regulation of the colonocyte cell cycle and gut motility and may also reduce the risk of large bowel cancer. We have shown that dietary butyrylated starch can deliver butyrate to the large bowel in a sustained manner. We hypothesized that ingestion of butyrylated starch increases large bowel butyrate levels and decreases colonic contractility. Groups of male Sprague-Dawley rats (n = 8) were fed AIN-93G-based diet containing a highly digestible low-amylose maize starch (LAMS) control or 5% or 10% butyrylated LAMS (LAMSB) for 10 days. We found that cecal but not colonic tissue weight as well as cecal and distal colonic digesta weights and fecal output were higher in LAMSB fed rats. Butyrylated LAMS lowered digesta pH throughout the large bowel. Cecal, proximal, and distal colonic butyrate pools and portal venous butyrate concentrations were higher in rats fed LAMSB. Electrically stimulated and receptor-dependent carbachol and prostaglandin E(2)-induced isotonic contractions were lower in isolated intact sections of proximal colon (P < .05) but not the terminal ileum after 10% LAMSB ingestion. These results demonstrated that elevation of butyrate levels in the large bowel of the rat correlated with reduction of contractile activity of the colonic musculature, which may assist in the reabsorption of water and minerals.

Half-logistic time constants as inotropic and lusitropic indices for four sequential phases of isometric tension curves in isolated rabbit and mouse papillary muscles

The waveforms of myocardial tension and left ventricular (LV) pressure curves are useful for evaluating myocardial and LV performance, and especially for inotropism and lusitropism. Recently, we found that half-logistic (h-L) functions provide better fits for the two partial rising and two partial falling phases of the isovolumic LV pressure curve compared to mono-exponential (m-E) functions, and that the h-L time constants for the four sequential phases are superior inotropic and lusitropic indices compared to the m-E time constants. In the present study, we tested the hypothesis that the four sequential phases of the isometric tension curves in mammalian cardiac muscles could be curve-fitted accurately using h-L functions. The h-L and m-E curve-fits were compared for the four phases of the isometric twitch tension curves in 7 isolated rabbit right ventricular and 15 isolated mouse LV papillary muscles. The isometric tension curves were evaluated in the four temporal phases: from the beginning of twitch stimulation to the maximum of the first order time derivative of tension (dF/dt(max)) (Phase I), from dF/dt(max) to the peak tension (Phase II), from the peak tension to the minimum of the first order time derivative of tension (dF/dt(min)) (Phase III), and from dF/dt(min) to the resting tension (Phase IV). The mean h-L correlation coefficients (r) of 0.9958, 0.9996, 0.9995, and 0.9999 in rabbit and 0.9950, 0.9996, 0.9994, and 0.9997 in mouse for Phases I, II, III, and IV, respectively, were higher than the respective m-E r-values (P < 0.001). The h-L function quantifies the amplitudes and time courses of the two partial rising and two partial falling phases of the isometric tension curve, and the h-L time constants for the four partial phases serve as accurate and useful indices for estimation of inotropic and lusitropic effects.

HYPOVOLEMIA DOES NOT AFFECT SPEED OF ISOVOLUMIC LEFT VENTRICULAR CONTRACTION AND RELAXATION IN EXCISED CANINE HEART

Hypovolemia results in hypotension due to a decrease in left ventricular (LV) stroke volume. We have showed a logistic relaxation time constant (tauL) that is a superior lusitropic index during the LV pressure (LVP) falling phase independent of LV preload compared with the conventional monoexponential relaxation time constant (tauE). In the present study, we investigated the effect of decreasing LV preload on tauL and tauE during the LV contraction and other relaxation phases. The isovolumic LVP curve was analyzed at LV Volumes (LVVs) of 18, 14, and 10 mL during 2-Hz pacing in seven excised, cross-circulated canine hearts. TauL and tauE were evaluated using logistic and monoexponential analyses of the four phases of the cardiac cycle: the period from the onset to the maximum time derivative of LVP (LV dP/dtmax), from LV dP/dtmax to peak LVP, from peak LVP to the minimum time derivative of LVP (LV dP/dtmin), and from LV dP/dtmin to LV end-diastolic pressure. TauL and tauE during the four phases did not change significantly with the decrease in LVV. During the change in LVV, the logistic function always fit significantly better compared with the monoexponential function. In conclusion, hypovolemia does not affect the speed of isovolumic LV contraction and relaxation. Each phase of the LVP curve is of a logistic nature. TauL is as a useful index for estimation of the speed of alteration during each phase of cardiac systole and diastole.

Integrative control of rectoanal reflex in guinea pigs through lumbar colonic nerves

The aim of the present study was to analyze the neuromodulation of rectoanal reflex activity by lumbar sympathetic nerves in guinea pigs. The mechanical activities of the rectum were recorded with a balloon connected to a pressure transducer, and those of the internal anal sphincter (IAS) were recorded with a custom-made strain gauge force transducer. Gradual and sustained rectal distension evoked the rectoanal reflex, causing cholinergic contractions of the rectum and synchronous nitrergic relaxations of the IAS. Section of the lumbar colonic nerves enhanced both rectal contractions and IAS relaxations. Section of the 13th thoracic cord abolished both rectal contractions and IAS relaxations, but section of the lumbar colonic nerves restored them. Lumbar sympathectomy and pithing sacral cords greatly diminished these rectal contractions and IAS relaxations, but the intrinsic reflex component remained. NG-nitro-L-arginine methyl ester enhanced the intrinsic reflex-mediated contraction of the rectum and abolished reflex-mediated relaxation of the IAS and converted into cholinergic contractions. The present results indicate that the extrinsic lumbar inhibitory outflow causes marked inhibition of the rectoanal reflex via the lumbar colonic nerves.