An aerodynamic valve in the avian primary bronchus.

The segmentum accelerans in geese is a constriction in the caudal end of the primary bronchus. Experimental evidence suggests that this part of the airway functions as an inspiratory aerodynamic valve, accelerating the incoming airstream past the ventrobronchial openings. The luminal diameter of the segmentum accelerans dilates in the presence of elevated CO2 levels, probably through relaxation of smooth muscle. Physiological control of the segmentum accelerans may permit inspiratory aerodynamic valving to be maintained throughout a wide range of ventilatory flows.     

A NEW RHEOCRICOTOPUS THIENEMANN & HARNISCHIA (DIPTERA: CHIRONOMIDAE) FROM TAIWAN PROVINCE CHINA

Abstract  Rheocricotopus (Psilocricotopus) taiwanensis sp. n. from Taiwan, China, is described as male imagines. The species is allied to R. (P.) chalybeatus (Edwards) but it is easily separated from the latter in lacking setae in all reins, much lower AR and more pronounced crista dorsalis in gonostylus. The genus is new to Taiwan Province, China. The specimen is deposited at the Department of Biology, Nankai University, Tianjin.     

Selected contribution: effects of ischemia-reperfusion on vascular contractility and alpha(1)-adrenergic-receptor signaling in the rat tail artery.

To determine the effects of ischemia-reperfusion (I/R) on alpha(1)-adrenergic-receptor (alpha(1)-AR) functions, alpha(1)-AR-mediated contraction, inositol phosphate (IP) accumulation, and alpha(1)-AR-G protein coupling were examined in the tail arteries of anesthetized rats after 60 min of ischemia and 60 min of reperfusion. The contractile response to norepinephrine (NE) was significantly increased after I/R, whereas the contractile response to KCl remained unchanged. This was accompanied by a 69% increase in NE-stimulated IP accumulation. Furthermore, receptor-stimulated coupling of alpha(1a)-AR to G alpha(q/11) proteins was increased, whereas the coupling of alpha(1b)-AR or alpha(1d)-AR to their G proteins was not altered by I/R. These changes in vascular alpha(1)-AR function occurred without concurrent alteration in expression levels of membrane alpha(1)-AR subtypes or in the associated G proteins. These data demonstrate that I/R increases alpha(1a)-AR-G(q/11) protein coupling and alpha(1)-AR-stimulated IP accumulation in the tail artery. The alterations in alpha(1)-AR signaling are associated with and may underlie the enhanced contractile response of the tail artery to adrenergic stimulation after I/R.     

The uptake and intracellular distribution of [35S]trithiomolybdate in bovine liver in vivo

[35S] trithiomolybdate was administered intravenously to a group of four steer at two dose rates, 1 and 26 mg Mo per animal. Radioactivity appeared rapidly in the liver and was distributed in all the subcellular fractions examined. Examination by Sephadex G-100 gel-filtration of the cytosol fraction showed that distinct 35S-binding protein peaks were present. The protein-bound radioactivity was displaceable and was identified as [35S]thiomolybdates. No radioactivity eluted with metallothionein, but 35S was associated with the high molecular weight copper fraction, eluted in the void volume of the column, which increased transiently after the administration of the higher dose. It was suggested that the presence of protein-bound thiomolybdates in the liver gave rise to new ligands, which altered the equilibrium of copper between the different metal-binding proteins. This might be similar to the alteration in the copper-binding of albumin produced by the presence of thiomolybdates.     

Interaction and combination of separate A and B chains of insulin effects of D-and L-tryptophan in position A1

The S-thiomethyl derivatives of insulin A chain with A1-Gly replaced by D- or L-Trp have been prepared and their respective interaction and combination with the S-thiomethyl B chain studied. The UV difference spectra of the mixed against the separated [Trp1]A chains with the B chain at pH 10.8 are similar to those obtained for the unmodified chains except that the 295-nm-negative peak for ionized Tyr residue appears to be less marked. Fluorescence studies show very little environmental changes at the A1-Trp residues when mixed with the B chain. The intact hormone with A1-Gly replaced by D-Trp is known to be considerably more active than the analog with L-Trp replacement. However, for both derivatives the resynthesis of the whole molecules correctly joined by disulfide bridges starting from the separated reduced chains, gives similar low yields as shown by HPLC analysis and by receptor-binding assay. The replacement of A1-Gly by D-Trp appears to affect the separated A chain more than the intact hormone and replacements at A1 by both D- and L-Trp probably lead to significant conformational changes of the A chain so as to prevent its correct pairing with the B chain.     

3H]AF-DX 116 labels subsets of muscarinic cholinergic receptors in rat brain and heart

The in vitro binding properties of the novel muscarinic antagonist [3H]AF-DX 116 were studied using a rapid filtration technique. Association and dissociation rates of [3H]AF-DX 116 binding were rapid at 25 degrees C (2.74 and 2.70 X 10(7) min-1 M-1 for K+1; 0.87 and 0.93 min-1 for k-1) but 20-40 times slower at 0-4 degrees C (0.13 and 0.096 X 10(7) min-1 M-1 for k+1; 0.031 and 0.022 min-1 for k-1 in cerebral cortical and cardiac membranes, respectively). Kinetic dissociation constants (Kds) were estimated to be 31.8 nM and 30.9 nM at 25 degrees C; 23.1 nM and 0-4 degrees C for the cerebral cortex and heart, respectively. In saturation studies, [3H]AF-DX 116 labeled 29 percent of the total [3H](-)QNB binding sites in the cerebral cortical membranes and 87 percent in the cardiac membranes, with Kd values of 28.9 nM and 17.9 nM, respectively. Muscarinic antagonists inhibited [3H]AF-DX 116 binding in a rank order of potency of atropine greater than dexetimide greater than AF-DX 116 greater than PZ greater than levetimide in both tissues. Except for PZ/[3H]AF-DX 116 and AF-DX 116/[3H]AF-DX 116 in the cerebral cortex, all the antagonist competition curves had Hill coefficients close to one. Carbachol and oxotremorine produced shallow inhibition curves against [3H]AF-DX 116 binding in both tissues. Regional distribution studies with [3H](-)QNB, [3H]PZ and [3H]AF-DX 116 showed that most of the muscarinic receptors in the cerebral cortex, hippocampus, nucleus accumbens and corpus striatum are of the M1 subtype while those in the brainstem, cerebellum and other lower brain regions are of the M2 subtype. These results indicate that [3H]AF-DX 116 is a useful probe for the study of heterogeneity of muscarinic cholinergic receptors.     

Postnatal changes in enzyme activities of rat myocardial adenine nucleotide catabolic pathway

Three catabolic enzymes, 5'-nucleotidase (5'NT), adenosine deaminase (ADA), purine nucleoside phosphorylase (PNP) and one anabolic enzyme, myokinase (MK) involved in adenine nucleotide (AN) metabolism were studied in myocardium from 4 to 105 day old rats. The specific enzyme activities (nmoles/min/mg protein) at day 4 were 35.3 for 5'NT, 28.4 for ADA, 43.3 for PNP, and 5 X 10(3) for MK. At day 7, 5'NT, activities rose to 450%; PNP and ADA 150%; and MK 120%; of the day 4 level. The activities of the three catabolic enzymes were elevated for one or two weeks then declined rapidly. By day 34, they were slightly above the adult values. MK activity displayed a different time course. It continued to increase slowly with age after the initial surge. Compared to the adult heart, the total activities of these catabolic enzymes in the one- to three-week-old heart were 30% to 220% higher. This transient elevation in AN catabolic enzyme activities may be related to active DNA synthesis and cell proliferation occurred in the rat myocardium during the same period.     

Interrelationship between estrogen and thyroxine on the release of luteinizing hormone and gonadotropin-releasing hormone in vitro

The present experiments were designed to study the interaction between estradiol benzoate (EB) and thyroxine (T4) given in vivo on the responsiveness of pituitary luteinizing hormone (LH) to gonadotropin-releasing hormone (GnRH) and the release of GnRH in vitro. Ovariectomized-thyroidectomized (Ovx-Tx) rats were injected s.c. with saline or T4 (2 micrograms/100 g b.wt), and oil or EB (0.1 microgram) once daily for 40 days following a 2 x 2 factorial design. All animals were then decapitated and blood samples were collected. Anterior pituitaries (APs) were incubated in vitro with and without 0.1 ng GnRH at 37 degrees C for 4 h. Mediobasal hypothalami (MBHs) were excised and then incubated with and without APs from Ovx donor rats. Concentrations of LH and GnRH in the medium and that of LH in the serum were measured by radioimmunoassay. The LH level in media containing MBHs and donor APs was used as the index of bioactive GnRH release. In Ovx-Tx rats, T4 injections reduced the serum LH concentration, the pituitary LH response to GnRH, and the bioactive as well as the immunoreactive GnRH release. The serum LH levels and the spontaneous as well as the GnRH-stimulated release of LH in vitro were suppressed in Ovx-Tx rats following administration of EB. By contrast, the serum LH concentration, as well as pituitary LH response to GnRH and GnRH release in vitro, were higher in the group treated with both T4 and EB than in that treated with saline and EB. These results suggest that the differential changes in the LH secretion after thyroidectomy of Ovx versus non-Ovx rats are due to an antagonistic effect between T4 and estrogen on the response of pituitary LH to GnRH, and the release of GnRH.