David W. Amory

Suppression of Spermatogenesis by Bisdichloroacetyldiamines Is Mediated by Inhibition of Testicular Retinoic Acid Biosynthesis

The bisdichloroacetyldiamine WIN 18,446 reversibly inhibits spermatogenesis in many species, including humans; however, the mechanism by which WIN 18,446 functions is unknown. As retinoic acid is essential for spermatogenesis, we hypothesized that WIN 18,446 might inhibit retinoic acid biosynthesis from retinol (vitamin A) within the testes by inhibiting the enzyme aldehyde dehydrogenase 1a2 (ALDH1a2). We studied the effect of WIN 18,446 on ALDH1a2 enzyme activity in vitro, and on spermatogenesis and fertility in vivo, in mature male rabbits for 16 weeks. WIN 18,446 markedly inhibited ALDH1a2 enzyme activity in vitro with an IC(50) of 0.3 μM. In vivo, the oral administration of 200 mg/kg WIN 18,446 to male rabbits for 16 weeks significantly reduced intratesticular concentrations of retinoic acid, severely impaired spermatogenesis, and caused infertility. Reduced concentrations of intratesticular retinoic acid were apparent after only 4 weeks of treatment and preceded the decrease in sperm counts and the loss of mature germ cells in tissue samples. Sperm counts and fertility recovered after treatment was discontinued. These findings demonstrate that bisdichloroacetyldiamines such as WIN 18,446 reversibly suppress spermatogenesis via inhibition of testicular retinoic acid biosynthesis by ALDH1a2. These findings suggest that ALDH1a2 is a promising target for the development of a reversible, nonhormonal male contraceptive.

Single fiber recording of the ventricular response to induced hypothermia in the anesthetized dog: correlation with multicellular parameters.

Ventricular membrane Potentials were recorded by the microelectrode technic in anesthetized, open-chest dogs. Concurrently, intraventricular pressure, electrocardiogram and esophageal temperature were recorded. Hypothermia was induced by an extracorporeal cooling method. Data on the parameters observed are presented for a temperature range from 38 to 22 C. The mean temperature for spontaneous ventricular fibrillation was approximately 22 C. Hypothermia increased single fiber action potential duration, primarily by prolonging the plateau phase. Depolarization and terminal repolarization were less affected. Action potential amplitude and resting potential were not changed. Change in action potential duration as a function of varying heart rate became more pronounced with cooling. A characteristic change in action potential shape during early repolarization became evident as hypothermia progressed. Hypothermic changes in the single fiber action potential are compared with changes in the electrocardiogram and the pressure curve. Recordings made from single fibers during hypothermic ventricular fibrillation showed a marked shortening in action potential duration.

Systemic and Regional Blood Flow during Epidural Anesthesia without Epinephrine in the Rhesus Monkey

The radioactive-microsphere technique was used to determine distribution of cardiac output and regional blood flow in rhesus monkeys before and 10, 20, 40, and 80 minutes after induction of epidural anesthesia with lidocaine (1 per cent) without epinephrine. Four monkeys were studied during low epidural anesthesia (sensory level T10) and five other monkeys were studied during high epidural anesthesia (sensory level T1). During T10 epidural anesthesia. During T1 epidural anesthesia, blood flow (per 100 g tissue) to the lower extremity was significantly increased 10 minutes after induction of anesthesia. There was no other significant change in regional blood flow during T10 epidural anesthesia. During T1 epidural anesthesia, blood flow to the heart was significantly reduced at 10 minutes, blood flow to the liver was significantly reduced at 10 and 40 minutes, blood flows to kidneys and miscellaneous organs (lymph nodes, salivary glands, etc.) were significantly reduced at 10, 20, and 40 minutes, and blood flow to the brain was significantly reduced throughout anesthesia. Vascular resistance in the lower extremity was reduced in each monkey following epidural anesthesia, indicating arteriolar dilatation. Also, during both levels of anesthesia, the lungs received an increased proportion of the microspheres, suggesting an increased periopheral arteriovenous shunting of microspheres due to the arteriolar dilatation.

Influence of hypothermic cardiopulmonary bypass on atrial natriuretic factor levels

Atrial natriuretic factor (ANF) is a peptide released from the heart in response to atrial distension. This peptide causes diuresis, vasodilatation, decreased blood pressure, and antagonizes the renin-aldosterone and antidiuretic hormone neuraxes. The influence of cardiopulmonary bypass and cardiac surgery on the circulation and release of ANF is unknown. Plasma ANF concentrations were therefore determined in patients undergoing coronary artery revascularization (CABG) and mitral valve replacement (MVR). Peptide levels were unchanged following anaesthetic induction. Plasma ANF concentrations decreased significantly during hypothermic (≤ 28° C) cardiopulmonary bypass in both patient groups. After 60 minutes of cardiac bypass, ANF declined from (mean ± SEM)512 ± 132 to 20± 6 pg · ml− (P < 0.05) during MVR, and from 178 ± 41 to 110 ± 48 pg·ml− during CABG (P < 0.05). Rewarming during bypass was associated with an increase in ANF concentration in both groups. Heparin anticoagulation and protamine reversal had no effect on immunoreactive ANF levels. In patients undergoing CABG, there was a linear relationship between plasma ANF concentration (pg · ml−1) and right atrial pressure (mmHg) prior to cardiopulmonary bypass (r = 0.86, P < 0.005). However, one and three hours after cardiopulmonary bypass there was no significant relationship between right atrial pressure and ANF plasma levels. These results suggest that reduction in plasma ANF concentration occurs during hypothermic cardiopulmonary bypass. Furthermore, the proportional relationship between atrial distension and circulating ANF concentration was altered following cardiac surgery.RésuméEn réponse à la distension de l’oreillette, le cœur libére un peptide, le facteur natriurétique de l’ oreillette (ANF), qui induit diurse et vasodilatation, diminue la tension artérielle et inhibe la libération de la rénine, de l’aldostésterone et de l’hormone anti-diurétique. Pour évaluer l’impact de la circulation extra-corporelle (CEC) et de la chirurgie cardiaque sur la sécrétion d’ANF, nous en avons mesuré la concentration plasmatique ([ANF]) lors de revascularisations coronariennes (pontage) et de remplacements de la valve mitrale (valvuloplastie). Dans les deux types d’interventions, les niveaux d’ANF, inchangés aprés l’induction anesthésique, diminuèrent significativement avec la CEC (temp. 28° C). Après 60 minutes sous CEC, la[ANF] était passé de 512 ± 132 à 20 ± 6 pg·ml−1 (P ≤ 0.05) dans le groupe « valvuloplastie » et de 178 ± 41 à 110 ± 48 pg·ml−1 (P≤ 0.05) dans le groupe « pontage ». La [ANF] augmentait pendant le richauffement sous CEC mais était indifférente à l’ anticoagulation par heparine et à son antagoniste, la protamine. Dans le groupe «pontage», nous avons observi une relation lineaire entre [ANF] et la pression de l’oreillette droite avant CEC (r = 0.86, P ≤ 0.05) mais, cette relation ne tenait plus, une heure et trois heures post-CEC. Il semble done qu’il y ait diminution de la concentration plasmatique d’ANF pendant la CEC hypothermique et qu’en plus il y ait perturbation du couple ANF-pression de l’oreillette apris la chirurgie cardiaque.

Regional blood flows during induced hypotension produced by nitroprusside or trimethaphan in the rhesus monkey.

In monkeys anesthetized with 70% nitrous oxide and 0.5% inspired halothane in oxygen, we measured changes in systemic hemodynamics and regional blood flows produced by nitroprusside and trimethaphan. Regional blood flow measurements were made using the radioactive microsphere technique. Control measurements were made before infusion of nitroprusside and trimethaphan into each animal in sequence in amounts adequate to reduce mean arterial pressure to approximately 55 ± 5 mm Hg. Measurements were made during each drug infusion after a stable period of hypotension lasting at least 30 min. During nitroprusside infusion, cerebral blood flow remained unchanged, but myocardial blood flow increased significantly. However, pressure-rate product, an indirect measure of myocardial oxygen consumption, was unchanged, implying that myocardial blood flow exceeded myocardial oxygen requirement. During trimethaphan infusion, cerebral blood flow decreased, although cerebral metabolic rate for oxygen was unchanged due to increased oxygen extraction by the brain. Trimethaphan also produced a decrease in myocardial blood flow that was in proportion to the decrease in myocardial oxygen requirement as indicated by pressure-rate product. Neither drug produced changes in renal or total hepatic blood flows. We conclude that brain oxygen reserve is decreased during hypotension induced by trimethaphan. Blood flows to other organs are not significantly impaired in monkeys during hypotension to a mean arterial pressure of approximately 55 mm Hg induced by either nitroprusside or trimethaphan.

Effects of ether anesthesia and surface-induced hypothermia on regional blood flow

Regional blood flow and distribution of cardiac output (CO) were evaluated by the radioactive microsphere technique in seven rhesus monkeys prior to anesthesia, following the induction of deep ether anesthesia and throughout the cooling course during surface-induced hypothermia to temperatures of 20 degrees C. As given, deep ether anesthesia alone significantly decreased CO 10% to 15% and output fraction (Qt) was decreased to the carcass, increased to the splanchnic circulation (although not statistically significant), and unchanged to other organs, while total vascular (TVR) and organ resistances were reduced. With the addition of cooling, CO progressively decreased. Individual organ Qts, however, did not change from anesthetized normothermic values; thus organ flows decreased parallel to the reduction of CO as cooling progressed. TVR and organ vascular resistances increased to levels in excess of 150% of anesthetized precooling values, apparently as the result of viscosity rather than vascular changes.

Effects of circulatory arrest and rewarming on regional blood flow during surface-induced hypothermia

Regional blood flow and distribution of cardiac output (CO) were evaluated by the radioactive microsphere technique in rhesus monkeys during surface rewarming following the induction of deep hypothermia (20 degrees C.) under deep ether anesthesia. A comparison of animals subjected to 30 minutes of circulatory arrest and those not arrested revealed cerebral, coronary, and renal vascular resistance and flow patterns consistent with a hyperemic response to circulatory arrest at 20 degrees C. Throughout rewarming cerebral and coronary absolute flows tended to be at or above the flows noted at comparable cooling temperatures in a previous study. Renal flow fraction (% Qt) were well preserved during rewarming to 30 degrees C., but a decrease was observed thereafter. Carcass (muscle, skin, bone) %Qt was also reduced following rewarming, especially in arrested animals. CO appeared to be similar to those noted at comparable cooling temperatures until 30 degrees C. during rewarming; thereafter, CO did not fully recover to awake control levels. These data suggest that regional flow is redistributed from the carcass and renal circulations to cerebral and coronary circulations in response to hemodynamic alterations during surface rewarming. It was concluded that autoregulative responses to both circulatory arrest and hemodynamic factors are elicited during surface rewarming from deep hypothermia to 20 degrees C. with the method described.

Lidocaine and Pentylenetetrazol Seizure Thresholds in Cats Are Not Reduced after Enflurane Anesthesia

Some previous reports indicate that the excitability of the brain may be increased for days following enflurane anesthesia. The authors investigated this possibility in cats by determining whether or not pentylenetetrazol- (Metrazol®) or lidocaine-seizure thresholds decreased after repeated enflurane exposure. The lidocaine-seizure threshold was bracketed in 4 cats, and the pentylenetetrazol-seizure threshold was bracketed in another 4 cats. Each cat was then exposed to 4 per cent enflurane for 2 hours on 4 successive days. Twenty-four hours after the last enflurane exposure, the cats were injected with the previously determined subthreshold dose of pentylenetetrazol (6.4 mg/kg, on the average) or lidocaine (7.8 mg/kg, on the average). No cat convulsed. It was therefore concluded that under our experimental conditions, repeated enflurane exposure does not increase the sensitivity to drugs which nonselectively excite the central nervous system (e.g., pentylenetetrazol) or to drugs which mimic temporal lobe epilepsy (e.g., lidocaine). This finding casts doubt that brain excitability is increased in the post-enflurane anesthetic period.

Systemic and Regional Blood Flow During Epidural Anesthesia with Epinephrine in the Rhesus Monkey

Hemodynamic and regional blood flow measurements were made in five rhesus monkeys before and 10, 20, 40 and 80 min after induction of high epidural anesthesia (T1) with lidocaine (1%) containing 1:200,000 epinephrine. Following induction of epidural anesthesia with epinephrine, there were significant decreases in heart rate, mean arterial pressure, cardiac output and myocardial and renal blood flow. The percentage of cardiac output received by the brain was significantly increased following epidural anesthesia with epinephrine, thus evidencing autoregulation to maintain cerebral blood flow. Vascular resistance in the lower extremity was significantly decreased during anesthesia, indicating arteriolar dilatation. Also, during anesthesia, the lungs received a significantly increased proportion of the microspheres, suggesting an increased peripheral arteriovenous shunting of microspheres due to the arteriolar dilatation.

Effect of total sympathetic blockade on plasma renin activity during surgery

The interaction of sympathetic blockade and decreased mean arterial pressure on plasma renin activity during surgery was studied in dogs. Plasma renin activity was measured during lumbar laminectomy before and after sympathetic blockade produced by subarachnoid spinal anaesthesia. Plasma renin activity was significantly increased during laminectomy. Twenty minutes after sympathetic blockade there were marked decreases in mean arterial pressure and plasma renin activity; but with mean arterial pressure continuing to decline, plasma renin activity showed moderate increases at 50 minutes after sympathetic blockade. It is concluded that increases in plasma renin activity seen during surgical operations can be attenuated by sympathetic blockade produced by subarachnoid or epidural spinal anaesthesia, although decreases in mean arterial pressure resulting from the sympathetic blockade continue to provide a stimulus for renin secretion.RéSUMéLes interactions d’un bloc sympathique et d’une diminution de la pression artérielle moyenne sur l’activité plasmatique de la rénine ont fait ’objet de cette étude effectuée chez le chien. A cette fin, l’activité de la rénine plasmatique a été mesurée au cours de laminectomies lombaires avant et après production d’un blocage sympathique par de rachi-anesthésie. On a observé une augmentation significative de l’activité de la rénine au cours des laminectomies. Des diminutions marquées de cette activité et de la pression artérielle moyenne étaient notées 20 minutes apres le bloc sympathique. La pression arterielle moyenne continuait a décroître alors que l’activité de la rénine était légèrement augmentée 50 minutes aprés le bloc. II est conclu que I’augmentation de l’activité plasmatique de la rénine observée au cours d’interventions chirurgicales peut être atténuée par un blocage sympathique (anesthésie rachidienne ou péridurale) bien que la diminution de la pression artérielle moyenne produite par le bloc sympathique contribue à stimuler la sécretion de rénine.