American Journal of Physiology 

About: American Journal of Physiology is an academic journal. The journal publishes majorly in the area(s): Blood pressure & Sodium. It has an ISSN identifier of 0002-9513. Over the lifetime, 23864 publications have been published receiving 728816 citations. The journal is also known as: Am. J. Physiol. & Am J Physiol.

A study of the adrenotropic receptors

Abstract: T HE adrenotropic receptors are those hypothetical structures or systems located in, on or near the muscle or gland cells affected by epinephrine. The concept of a receptive mechanism was introduced by Langley (I, 2) to explain the action of curare on skeletal muscle. Dale was probably the first to make significant use of the receptor concept in connection with the sympathetic nervous system. In his classical paper (3) on the sympatholytic action of the ergot alkaloids, he recognized that what he called the sympathetic myoneural junction could also be called 'the receptive mechanism for adrenaline'; and he used this mechanism to explain the fact that the ergot alkaloids prevented only the motor (excitatory) actions of epinephrine and had no effect on the inhibitory actions of epinephrine or on the excitatory actions of barium or pituitrin. The adrenotropic receptors have been considered to be of two classes, those whose action results in excitation and those whose action results in inhibition of the eff ector cells. Experiments described in this paper indicate that although there are two kinds of adrenotropic receptors they cannot be classified simply as excitatory or inhibitory since each kind of receptor may have either action depending upon where it is found. The evidence for these conclusions is, in brief, that a series of six sympa-thomimetic amines has one order of potency-r, 2, 3, 4, 5, 6-on the following functions: vasoconstriction, excitation of the uterus and ureters, contraction of the nictitating membrane, dilation of the pupil and inhibition of the gut. In contrast, this same series of amines has an entirely different order of potency-z, 4, 6, 5, 3, Ion the following functions: vasodilation, inhibition of the uterus and myocardial stimulation. The variations in activity could be due to any or all of three factors: a) quantitative differences in potency, b) qualitatively different effects or c) differences due entirely to the experimental methods used. If the last Tao factors are controlled as much as possible by the selection of the amines and by using suitable experimental techniques, then the variations in activity are presumably due to actual differences in the receptors involved. Tentatively the first kind of receptor has been called the alpha adrenotropic receptor and the second kind the beta receptor. This concept of two fundamental types of receptors is directly opposed to the concept of two mediator substances (sympathin E and sympathin I) as propounded by …

Hyperfiltration in remnant nephrons : A potentially adverse response to renal ablation

Abstract: Micropuncture studies were performed in three groups of male Munich-Wistar rats 1 wk after surgery: group I, eight control rats that underwent laparotomy and were fed a normal diet; group II, nine rats that underwent right nephrectomy and segmental infarction of five-sixths of the left kidney and were fed a normal diet; and group III, seven rats that underwent the same renal ablative procedure and were fed a low protein diet. Single nephron glomerular filtration rate (SNGFR) was higher in the remnant kidney of group II rats compared with group I rats due to higher average values for mean glomerular transcapillary hydraulic pressure difference (delta P) and initial glomerular plasma flow rate (QA) in group II. Glomeruli in remnant kidneys of group II showed striking alterations in morphology, including epithelial cell protein reabsorption droplets, foot process fusion, and mesangial expansion. Group III rats demonstrated a mean SNGFR not statistically different from that of group I, but significantly less than that of group II rats. This lack of absolute hyperfiltration in remnant glomeruli of group III rats relative to group I obtained because QA and delta P did not increase above values found in group I. The glomerular structural lesions seen in group II were also largely attenuated in group III. These studies demonstrate that alterations in glomerular hemodynamics associated with renal ablation are accompanied by structural lesions and suggest that sustained single nephron hyperfiltration may have maladaptive consequences by damaging remnant glomeruli.

Brain uptake of radiolabeled amino acids, amines, and hexoses after arterial injection

Abstract: OILIENDORF, WILLIAM EL Brain uptake of radiolaMed amino acids, nmines, and hexoses after arterial injection. Am. J. Physiol. 2 2 I(6) : 16294639. 1971 .-The loss of a 14C-labeled test substance to brain during a single capillary passage following rapid injection into the rat common carotid artery was measured relative to a simultaneously injected highly diffusible reference, 3HOHW Twenty-eight amino acids, thirteen amines, seven hexoses, and 5 relatively nondiffusible substances were studied. Amino acid uptakes ranged from unmeasurably low to 55%. Essential nutritional amino acid uptake was greater than nonessential. TWO blood-brain barrier (BBB) carrier systems for amino acids were identified. Putative transmitter substances were much less taken up by brain than precursors. Saturability of D-glucose uptake was demonstrated and evidence presented that all of the five hexoses measurably taken up by brain shared a common carrier. Nonmetabolized cycloleucine and 3-O-methylglucose showed saturable uptakes. Amino acid uptake was incompletely stereo-specific whereas glucose uptake was stereospecific. Phlorizin inhibits brain uptake of D-glucose. Relative BBB permeabilities to many of the test substances resemble red-cell permeabilities. Carrier systems for amino acids are independent of the glucose carrier.

Hemodynamic determinants of oxygen consumption of the heart with special reference to the tension-time index.

Abstract: The hemodynamic determinants of myocardial oxygen utilization were ascertained in the isolated, metabolically supported, nonfailing canine heart. The primary determinant was found to be the total t...

Mechanical work in terrestrial locomotion: two basic mechanisms for minimizing energy expenditure

Abstract: The work done during each step to lift and to reaccelerate (in the forward direction) and center of mass has been measured during locomotion in bipeds (rhea and turkey), quadrupeds (dogs, stump-tai...