Effect of ammonia on survival and adenylate energy charge in the shrimp Palaemonetes varians.

Shrimps Palaemonetes varians were submitted to lethal and sublethal concentrations of ammonia in order to measure lethality, ATP and adenylate nucleotide levels, and adenylate energy charge (AEC) index. LC50 was of about 3 mg/liter of ammonia. Adenylate measurements were performed over a period of 14 days and for two different concentrations. A population submitted to 0.5 mg/liter of ammonia exhibited high survival and a marked consumption of ATP, whereas high mortality and disordered ATP metabolism are the characteristics of the population submitted to 3 mg/liter of ammonia. An homeostatic model was applied in order to explain the significance of the AEC signal. Here, AEC is proposed as a measure of the limits of active response of an organism to environmental stress.

[Subarachnoid anesthesia with Sprotte 24-G needle in ambulatory surgery]. / Anestesia subaracnoidea con ago di Sprotte 24-G in chirurgia ambulatoriale.

In order to evaluate the possibility of using a selective subarachnoid anesthesia in ambulatory surgery we studied its feasibility with a Sprotte needle 24 G in 103 patients (range 15-67 years) undergoing a knee joint arthroscopy. The subarachnoid anesthesia was achieved with Sprotte needle 24 G with introducer with patient on lateral decubitus. Hyperbaric bupivacaine 1% (0.05 mg/cm height) was used in order to obtain a selective homolateral metameric anesthesia between L1 and S3. The numbers of attempts were 1.29 (range 1-4). We involved the homolateral determatomeres in 94% of our attempts, adding a weak anesthetic action on contralateral ones. In the remaining 6% of the patients the anesthesia was bilateral and extending in an overlying manner. Anesthesia was adequate for the time needed to perform all the surgical procedures. Nevertheless in 3 patients the tourniquet was painful. We registered systemic hypotension only in 2% of the patients (a reduced systolic pressure value > 30%). No cases of postdural puncture headache were registered. Non postural atypical headache was seem in 3.9% of the patients. Urinary retention necessitating catheterization was noted only in 3 cases. A weak backache was revealed in 8.8%. When interviewed after surgery, 98% of our patients fulfilled the technique. In spite of technical difficulties that the use of the Sprotte needle may present, the selective subarachnoid anesthesia may be a safe alternative to the other anesthetic procedures for ambulatory surgery of the legs.

On the role of neural mechanisms in the cardiocirculatory inhibitory action of alpha-human atrial natriuretic peptide in the anesthetized rabbit.

The effects induced by alpha-human 28-amino acid residue atrial natriuretic peptide (alpha-hANP) on arterial pressure, heart rate and vascular resistance, measured as hindlimb perfusion pressure (HPP), were examined in anesthetized rabbits. In particular, the involvement of the autonomic nervous system in mediating the cardiocirculatory effects of alpha-hANP was investigated. Intravenous alpha-hANP (8 micrograms/kg, bolus injection) in anesthetized rabbits caused a sustained decrease in atrial pressure, a transient decrease in HPP and no significant changes in heart rate. After sinoaortic denervation, alpha-hANP produced a greater decrease in arterial pressure and in hindlimb vascular resistance and also a consistent decrease in heart rate. Bilateral vagotomy did not significantly alter the cardiocirculatory responses to alpha-hANP in either normal or in sinoaortic denervated rabbits. Intravenous infusion of alpha-hANP (2 micrograms/kg bolus + 0.2 micrograms/kg per min) did not substantially change the baroreflex cardiocirculatory responses to loading and unloading carotid and aortic baroreceptors with bilateral carotid occlusion and phenylephrine or nitroglycerin bolus injection. In addition, alpha-hANP infusion did not modify the cardiovascular reflex responses to chemical stimulation of neural receptors (sensory endings of group III and IV somatic afferents) in the hindlimb muscles which are primarily mediated by sympathetic nerves in the anesthetized rabbit. Pharmacological blockade of the autonomic nervous system with atropine and guanethidine did not reduce the hypotensive and bradycardic effects caused by alpha-hANP in sinoaortic denervated animals. The results indicate that in anesthetized rabbits: (1) alpha-hANP can induce inhibitory cardiocirculatory responses (hypotension, bradycardia, musculocutaneous vasodilation) which are consistently offset by the sinoaortic baroreceptor system; (2) alpha-hANP does not alter the reflex control of arterial pressure and heart rate by arterial baroreceptors and muscle chemosensitive receptors; (3) activation of cardiopulmonary vagally-mediated depressor reflexes does not contribute to the inhibitory cardiovascular action of alpha-hANP; and (4) inhibitory effects on sympathetic activity do not constitute a significant component of the cardiocirculatory action of alpha-hANP.

[Integrated cardiorespiratory changes induced by chemical stimulation of muscular receptors]. / Modificazioni integrate cardiorespiratorie indotte da stimolazione chimica di recettori muscolari.

Muscular exercise is accompanied by evident and perfectly matched cardiovascular and respiratory adjustments to avoid changes in arterial blood gases. The mechanisms responsible for this perfect regulation have not yet been defined. Our previous experimental investigations have shown that a consistent rate of cardiorespiratory reflex responses to exercise is caused by chemosensitive muscular receptors activation. The 2 different types of classical muscular exercise (rhythmic and isometric exercise) are joined with the 2 different patterns of cardiorespiratory reflex responses attributed in our opinion to the activation of 2 different kinds of muscle receptors (K and P). It has been observed that the increase in ventilation (VE), elicited by activation of both types of chemoreceptors during muscular experimental exercise is not accompanied by significant variations of partial pressure of CO2 (PaCO2) in the arterial blood (isocapnic hyperpnea). This suggest that muscular chemoreceptor activation during physical exercise determines an adequate cardiopulmonary matching. The main purpose of the present study has been to verify, in anesthetized rabbits, if also the chemical activation of muscular receptors was able to evoke reflexly an adequate degree of cardiopulmonary matching. The ventilation reflex changes and the concomitant variations of PaCO2 induced by injection of bradikinin (BK 250 ng) and hypertonic solutions (NaCl 10% 1 ml) in femoral artery have been evaluated in 10 anesthetized rabbits. The PaCO2 modifications observed during reflex hyperpnea have been compared with those recorded during hyperpnea induced by artificial ventilation.(ABSTRACT TRUNCATED AT 250 WORDS)