Beat-to-beat modulation of heart rate is coupled to coronary perfusion pressure in the isolated heart.

A goal of clinicians caring for heart transplant recipients has been to use heart rate variability as a noninvasive means of diagnosing graft rejection. The determinants of beat-to-beat variability in the surgically denervated heart have yet to be elucidated. We used an isolated, blood buffer-perfused porcine heart preparation to quantitatively assess the relationship between coronary perfusion and sinus node automaticity. Hearts (n = 9) were suspended in a Langendorff preparation, and heart rate (HR) fluctuations were quantified while perfusion pressure was modulated between 70/50, 80/60, 90/70, and 100/80 mmHg at 0.067 Hz. In 32 of 32 recordings, the cross spectrum of perfusion pressure vs. HR showed the largest peak centered at 0.067 Hz. In eight of nine experiments during nonpulsatile perfusion, HR accelerated as perfusion pressure was increased from 40 to 110 mmHg (mean increase 24.2 +/- 3.0 beats/min). HR increased 0.34 beats/min per mmHg increase in perfusion pressure (least squares linear regression y = -25.8 mmHg + 0.34x; r = 0.88, P < 0.0001). Administration of low- and high-dose nitroglycerin (Ntg) resulted in a modest increase in flow but produced a significant decrease in HR and blunted the response of HR to changes in perfusion pressure (HR increase 0.26 beats. min-1. mmHg-1, r = 0.87, P < 0.0001 after low-dose Ntg; 0.25 beats. min-1. mmHg-1, r = 0.78, P < 0.0001 after high-dose Ntg). These experiments suggest that sinus node discharge in the isolated perfused heart is mechanically coupled to perfusion pressure on a beat-to-beat basis.

Respiratory sinus dysrhythmia persists in transplanted human hearts following autonomic blockade.

1. The present study was performed to test whether beat-to-beat cardiovascular control in cardiac allograft recipients resides in cholinergic and/or adrenergic nerves that are intrinsic to the heart. 2. Heart rate (HR) fluctuations synchronous with respiration during spontaneous, double tidal volume and metronome-synchronized breathing were quantified in 13 human heart transplant recipients. We also examined the effects of sequential cholinergic and beta-adrenoceptor (combined) autonomic blockade on respiratory sinus arrhythmia (RSA). We computed RSA amplitude and the correlation between respiration and changes in HR (cardiopulmonary synchronization; CPS). Group means were compared using repeated-measures analysis of variance. Transplant recipients served as their own controls. 3. In the basal state, moderate RSA amplitude and CPS were observed. During cholinergic and combined blockade, we observed no significant change in RSA amplitude, whereas CPS increased significantly during combined blockade (P < 0.05). The amplitude of RSA increased during respiration at double baseline tidal volume, but not at any of the other breathing manoeuvres (P < 0.01). In contrast, CPS increased significantly during both patterned breathing manoeuvres. No significant correlation was seen between mean right atrial pressure and RSA amplitude. In 23% of subjects with low CPS, HR oscillated with arterial pressure. These oscillations were independent of respiration. During all three patterns of respiration, a significant inverse correlation was observed between CPS and pulse pressure (r = -0.53 to -0.73). Thus, as the amplitude of pulse pressure increased, respiration accounted for a smaller percentage of HR variation. 4. In conclusion, RSA persists and the magnitude of CPS increases following combined autonomic blockade. These studies suggest that while RSA after cardiac transplantation is not cholinergically or adrenergically mediated, it may be related to mechanical stretch of the sinus node caused by changes in intrathoracic pressure and perfusion pressure.

Membrane glycoproteins from spermatozoa: partial characterization of an integral Mr = approximately 24,000 molecule from rat spermatozoa that is glycosylated during epididymal maturation.

Spermatozoa from the rat cauda epididymidis were treated with either the galactose oxidase-NaB[3H]4 or the NaIO4-NaB [3H]4 technique to label cell surface moieties of galactose and sialic acid, respectively. Following extraction with 40 mM octyl-beta-D-glucopyranoside (OBG), electrophoresis in sodium dodecylsulfate-polyacrylamide gels (SDS-PAGE) revealed a single radioactive peak migrating at Mr = approximately 24,000 in 11.2%, 14% and 16.8% tube gels. SDS-PAGE of the same OBG extract on 5.6% and 14% gels showed that this molecule was the same as that reported elsewhere, having a molecular weight varying from 32,000 to 37,000. The amount of labeled molecule extracted with 8 M urea or with 6 M guanidine-HCl was 30 and 50%, respectively, of that achieved with OBG. However, when labeled sperm were treated under other conditions (at pH 8, pH 3, 0.1-3 M NaCl [at pH 7.2], 5 mM ethylenediaminetetraacetic acid [EDTA], 20-200 mM dithiothreitol or 20-200 mM betamercaptoethanol, at varying temperatures and extraction times), the amount of labeled molecule extracted was less than 1% of that obtained with OBG. The molecule aggregates in aqueous buffers, as shown by chromatography using Sephadex G-100 and by centrifugation through a sucrose density gradient. Analysis by charge-shift electrophoresis suggested that the molecule contains an exposed hydrophobic domain(s). Mild trypsin treatment released all the labeled carbohydrate with the majority of the label attached to a Mr = 10,000 fragment. These data support the hypothesis that the molecule is an integral membrane glycoprotein, and suggest that it is only partially buried in the lipid matrix of the plasma membrane.

Synthesis and secretion of proteins in vitro by isolated epithelial strips from the proximal and distal vas deferens of the rat.

Epithelial strips of rat vas deferens were isolated by a new technique and used to study differences in protein synthesis and secretion between morphologically defined segments of the vas deferens. The isolated strips were viable as judged by linear oxygen uptake over the incubation period and by preservation of structure. Epithelium from the proximal vas deferens incorporated more labelled amino acids into cytosolic (P less than 0.02) and incubation medium (P less than 0.01) proteins than did epithelium from distal vas deferens; this incorporation was inhibited by cycloheximide. Although some of the incubation medium proteins arose by leakage from damaged cells, specific protein secretion was indicated by differences in SDS-PAGE autoradiogram banding patterns and by differences in glycosylation between proteins in the incubation medium and those in the cytosol. Thus, the former contained more label from [14C]galactose incorporation than did cytosolic proteins (proximal: P less than 0.05; distal: P less than 0.005).

Rapid compensatory hypertrophy of the lamb testis after neonatal hemiorchidectomy: endocrine and light microscopical morphometric analyses.

The testis mass of lambs hemiorchidectomized (HO) within 1 week of birth exceeded that of control testes by 23%, 67%, and 114% at 4, 8, and 12 weeks; the epididymis was 39% heavier than control epididymides by 12 weeks. The seminiferous tubular mass in HO testes grew at a faster rate than in control testes to achieve full compensation by about 10 weeks; Sertoli cell division was augmented in the 1- to 4 week phase and Sertoli cell cytoplasm increased throughout. The major growth response of the interstitium of HO testes occurred in the 1- to 4 week period but did not obtain full compensation by 12 weeks; the vascular component responded to HO by rapid growth in the 8- to 12 week period. There was a low incidence of division amongst gonocytes (prespermatogonia) in both groups of lambs but at 12 weeks spermatogonial mitoses, spermatocytes, and tubular lumina were present in four out of four HO tests but only one of three control testes. In the same lambs, HO induced an immediate increase in circulating plasma concentrations of FSH to 3-4 x control values at 8 weeks, which were then suppressed to near control values by 10 weeks. Apart from transient increases in LH (at 4-5 weeks) and testosterone (6-7 weeks) above control values, there were no differences between HO and control lambs in the circulating concentrations of any other hormone measured (LH, GH, TSH, PRL, and testosterone). The evidence suggests that the major prepubertal influence on testicular development and growth in lambs is the FSH-provoked response of the Sertoli cells.