B. V. Rama Sastry

Techniques to study human placental transport

Pregnancy in the 20th century involves women of many age groups from early teens to the fourth or fifth decade. Modern medicine and in vitro fertilization techniques have increased options for pregnancy and childbirth. Pregnancy is a dynamic state, and medical concerns may involve disorders of the fetus and mother requiring medications and special nutrients. Therefore, different techniques have been developed to evaluate the placental transfer of drugs and nutrients using tissues and cells derived from human placenta. These include (a) isolated tissues and cells to study placental transport, (b) primary and malignant trophoblast cell cultures and (c) biophysical methods for studying placental transport. Also, convenient study models have been developed to evaluate placental transfer of safe drugs in pregnant women. Some of the drugs studied by these techniques and models include (a) anesthetics and pain medications used during delivery, (b) antibiotics and anti-bacterials used to cure infections, (c) drugs abused by pregnant women and (d) nutrients required for proper fetal growth. Placental transfer and exchange mechanisms are complicated processes, and in vitro models reflect only partially the equilibria that exist among mother, placenta and fetus. The perfused cotyledon model is elegant and simple but gives only restricted information. Isolated placental tissues give useful information about the pharmacological effects of drugs. Metabolic studies using human placental models provide information on the metabolism of a drug during placental transfer and accumulation of the drug or its metabolite in the placenta or fetal circulation. Several studies on the transplacental passage of drugs exist but many questions regarding the transfer of drugs between the maternal and fetal circulations and clearance of drugs from fetal circulation have yet to be answered. This article reviews in vitro and in vivo methods for evaluation of transplacental transport of drugs and their current effectiveness to obtain clinically useful data.

Human placental cholinergic system

The occurrence of acetylcholine (ACh)-like activity in human placenta, a tissue without innervation, has been known for more than 60 years. However, the non-neuronal functions of ACh in human placenta are not clearly understood. The components of the cholinergic system-ACh, choline acetyltransferase, acetylcholinesterase, butyrylcholinesterase, muscarinic receptors, and nicotinic receptors--in human placenta have been demonstrated by unequivocal methods. Primate placentae store and release ACh by mechanisms similar to those of nervous tissue. However, there are many gaps in our knowledge, which include: (a) endogenous quaternary ammonium compounds other than ACh in human placental extracts; (b) the specificity of placental enzymes; (c) the subtypes and structures of placental muscarinic and nicotinic receptors; and (d) the significance of placental alpha-bungarotoxin binding proteins, ACh receptor stimulation-cellular signaling by second messengers, and activation of immediate early target genes (C-fos, C-jun) encoding transcription factors. Several hypothetical non-neuronal functions of ACh in placenta have been postulated based upon available experimental evidence. These include: (a) regulation of blood flow and fluid volume in placental vessels; (b) opening and closing of trophoblastic channels; (c) induction of contractile properties to myofibroblasts; (d) facilitation of amino acid transport necessary for fetal growth across placenta; (e) release of placental hormones; and (f) modulation of the formation of myometrial and placental prostaglandins in human parturition. All of these roles are reasonable, and some of these roles mav turn out to be linked to one another to influence or maintain placental function.

Immunoreactive substance P is decreased in saliva of patients with chronic back pain syndromes

Substance P, a neuropeptide associated with pain perception, is widely distributed in the central nervous system and is decreased in the cerebrospinal fluid of chronic pain patients as compared with that of healthy human volunteers. In this study, we have demonstrated the presence of immunoreactive substance P in saliva and further, that both saliva and plasma levels of immunoreactive substance P are lower in patients with chronic low back pain than in healthy human volunteers. To our knowledge, this is the first time that substance P has been identified in human saliva. These findings, together with the noninvasive nature of saliva collection, suggest that substance P in saliva may be useful as an alternative neurochemical correlate of chronic low back pain when collection of cerebrospinal fluid and plasma samples for substance P analysis is unacceptable or inappropriate.

NEUROPHARMACOLOGY OF NICOTINE: EFFECTS ON THE AUTOREGULATION OF ACETYLCHOLINE RELEASE BY SUBSTANCE P AND METHIONINE ENKEPHALIN IN RODENT CEREBRAL SLICES AND TOXICOLOGICAL IMPLICATIONS

1. The neuronal release of acetylcholine (ACh) and its autoregulation by neuromodulators, substance P (SP) and methionine enkephalin (MEK), have been studied using super‐fused rodent cerebral slices. Nicotine exerts significant effects on autoregulation of ACh release, which may have toxicological implications.

The inhibitory effect of metoclopramide on plasma cholinesterase activity

The in vitro effect of metoclopramide on plasma cholinesterase (PCHE) activity was studied to investigate a mechamistn for metoclopramide-induced prolongation of succinylcholine action. The mean PCHE of the control samples was 0.86 ° 0.02 unit·ml-1. PCHE activity in the presence of metoclopramide, at concentrations of 0.05, 0.10, 0.50,1.0, 2.5 and 5.0 μg·ml-1, was reduced to 0.78 ± 0.02, 0.69 ± 0.04,0.50 ± 0.03,0.39 ± 0.02, 0.24 ± 0.01 and 0.15 ± 0.01 unit ·ml-1, respectively. Our data demonstrated that PCHE activity was significantly depressed by metoclopramide at all concentrations studied (p < 0.001). Our data also show that the concentration of metoclopramide required to inhibit 50 per cent of PCHE activity (I50) was 0.8 μg·ml-1 (2.4 × 10-6 M). We recommend caution when succinylcholine and or ester type local anaesthetics are administered to patients who are also receiving metoclopramide, especially in high doses.RésuméĽeffet in vitro de la métoclopramide sur ľactivité de la cholinestérase plasmatique (PCHE) a été étudié afin ďinvestiguer le mécanisme de la prolongation de ľaction de la succinylcholine induite par la métoclopramide. La valeur moyenne des échantillons de contrôle de PCHE était de 0.86 ± 0.02 unités · ml-1. Ľactivité du PCHE en présence de métoclopramide à des concentrations de 0.05, 0.10, 0.50,1.0. 2.5 et 5.0 μg·ml-1, a été réduiteà0.78 ± 0.02, 0.69 ± 0.04, 0.50 ± 0.03, 0.39 ± 0.02, 0.24 ± 0.01 et 0.15 ± 0.01 unités·ml-1 respectivement. Nos données ont démontré que ľactivité de la PCHE était significativement diminuée par la métoclopramide à toutes les concentrations étudiées (p < 0.001). Nos données ont aussi démontré que la concentration de métoclopramide requise afin ďinhiber 50 pour cent de ľactivité de la PCHE (150) était de 0.8 μg · ml-1 (2.4 × 10-6 M). On recommande la précaution quand la succinylcholine ou anesthésique local type ester est administré aux patients qui reçoivent aussi la métoclopramide, spécialement à hautes doses.

In vitro effects of fluoride and bromide on pseudocholinesterase and acetylcholinesterase activities

The in vitroeffects of two metabolites ofinhalational anaesthetics, fluoride and bromide, on pseudocholinesterase (PCHE) and acetylcholinesterase (ACHE) activities in the blood samples of seven healthy patients were studied. The PCHE and ACHE activities were determined by kinetic spectrophotometric methods. Fluoride at the levels achieved with clinical concentrations of enjlurane and sevoflurane (25–75 μM · L−1) inhibited PCHE activity by 28–65 per cent (P < 0.01) and ACHE activity by less than five per cent (P > 0.05). Bromide at the levels achieved with clinical concentrations ofinhalational anaesthetics had no significant effect on either PCHE or ACHE activity. We recommend caution when succinylcholine and/or ester type local anaesthetics are used in the immediate postoperative period following enflurane or sevoflurane anaesthesia. We also recommend that blood drawing for PCHE activity be delayed at least until 24 hr following enflurane or sevoflurane anaesthesia.RésuméLes effets in vitrode deux métabolites anesthésiques d’inhalation, le fluorure el le bromure sur les activités de la pseudocho-linesterase (PCHE) el l’acetylcholinesterase (ACHE) out été étudié sur les échantillons sanguins de sept patients en bonne sante. Les activités de la PCHE et l’ACHE out été déterminées par spectrophotométrie. Les niveaitx de fluorure atteints avec des concentrations d’enjlurane et de sevoflurane à des concen-trations utilisees en clinique (25–75 μM · L−1) out inhibé l’activite de la PCHE de 28–65 pour cent (P < 0.0l) et l’activité de l’ACHE de moins de cinq pour cent (P > 0.05). Les niveaux de bromure atteints aux concentrations anesthesiques utilisees en clinique n’ont eu aucun effet significatif sur les activites de la PCHE ou de l’ACHE. On recommande la précaution lors de l’utilisation de la succinylcholine etlou les anesthésiques locaux dans la période post-opératoire immédiate après l’anesthésique à l’enflurane ou le sevoflurane. On recommande aussi que la prise d’échantillon sanguin pour l’activite de la PCHE soit retardée d’au moins 24 heures après l’anesthésie à l’enflurane ou la sevoflurane.

Tobacco Smoking by Pregnant Women Disturbances in Metabolism of Branched Chain Amino Acids and Fetal Growtha

Pregnancy alone lowered the plasma AA concentrations of ileu, leu, and val when compared to their concentrations in nonpregnant nonsmokers. Plasma concentrations of val, ileu, and leu were significantly higher in pregnant smokers than in pregnant nonsmokers. Therefore, the utilization of BCAA was more reduced in pregnant smokers than that which could be predicted from plasma AA concentrations of nonpregnant nonsmokers.

Substance P in Human Spermatozoa and Modulation of Sperm Motility by Substance P and Its Antagonists

There are similarities in the distribution of Substance P (SP) and enkephalins in the central and peripheral nervous systems. SP and methionine enkephalin (MEK) exhibited opposing effects on nociception, uptake of Ca++ ions by the nervous tissue, release of ACh and modulation of cholinergic function [1–3]. Peripheral branches of certain primary-afferent neurons liberated SP as a neurotransmitter in autonomic post-ganglionic cells and caused long-lasting increase in the excitability of ganghon cells to the primary transmitter, ACh [3]. The male genital system, its glands (seminal vesicles prostate, epididymis) and plexus (vesical, prostatic, cavernous) have rich autonomic and sensory or afferent innervation. However, little information is available about the role of SP in the male genital system.

Metabolic fate of 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine by human spermatozoa: biosynthesis and biodegradation.

Human spermatozoa can synthesise 1-alkyl-2-acetyl-glycerophosphocholine (AAGPC) in small amount by acetyltransferase (AT) in absence of any stimulus, but can actively catabolise it by acetylhydrolase (HY). Seminal plasma, on the other hand, was devoid of anabolic enzyme albeit enrich in catabolic enzyme, suggesting as an active site for biodegradation of AAGPC secreted by spermatozoa. Both, AT and HY exhibited pH-optima in range of 7.0-7.6 at which spermatozoa are maximum viable and motile. Ionophore A23187 and EGTA inhibited AT, reversibly, whereas HY was inhibited by BSA, calcium-channel blockers, and phospholipase A2-inhibitors. Effect of aging-time on ejaculates exhibited decreased AT activity with increased HY activity along with unchanged calcium content of spermatozoa. Serotonin in vitro studies showed a pro-aggregator role on agglutination of spermatozoa. Viscid/long liquefaction time ejaculates exhibited raised AT activity and calcium contents with decreased HY activity in spermatozoa and high degree of agglutination. Studies with dithiothreitol-treatment indeed helped in liquefaction but levels of both enzymes remained status quo, suggesting existence of both pathways: remodelling of membrane phospholipids and de novo synthesis of AAGPC in spermatozoa, earlier being pre-dominant. We have proposed a role of AAGPC-Serotonin-Calcium in agglutination and liquefaction of spermatozoa, a vital aspect in normal fertility.

Aging-Induced Changes in the Autoregulation of Acetylcholine Release in the Rat Brain

Senile dementia of Alzheimer type (SDAT) is a disease of mid- or late life, and about 3 to 4% of the population above 65 years of age is estimated to be afflicted by this progressive dementia.’ One of the main characteristics of this disease is a decline in such cognitive abilities as memory and learning.’ The decline in recent memory seems to be a common characteristic of aging in mammals including humans, non-human primates, and rodents. In humans, this impairment is exacerbated by SDAT. Although the reasons for this cognitive loss in aged or demented subjects are not fully understood, there is evidence that deficits in central cholinergic transmission play an important role.1,3 Postmortem samples from cortical regions of Alzheimer’s Disease (AD) patients have shown decreases of greater than 50% in the activity of choline acetyltransferase (ChAT), the enzyme that catalyzes the final step in the synthesis of acetylcholine (ACh). Scopolamine, an anticholinergic agent, causes memory defects in young adult volunteers. Physostigmine causes memory and thinking disturbances in human volunteers by preventing the hydrolysis of ACh, which accumulates to reach inhibitory concentrations at muscarinic receptors.