Somatostatin and insulin secretion due to common mechanisms by a new hypoglycemic agent, A-4166, in perfused rat pancreas

N-[(trans-4-isopropylcyclohexyl)-carbonyl]-D-phenylalanine (A-4166) is a nonsulfonylurea hypoglycemic agent that decreases blood glucose levels in nondiabetic and diabetic animals. In the present study, we attempted to determine the effect of A-4166 on hormone secretion from the in vitro-perfused rat pancreas and to examine the underlying secretory mechanisms. In the presence of basal glucose (3 mmol/L), A-4166 markedly stimulated insulin and somatostatin release in a concentration-dependent manner over 0.03 to 3 mmol/L. A sulfonylurea, tolbutamide, also stimulated insulin and somatostatin release. A-4166 and tolbutamide elevated the level of glucagon release; however, the change lacked a clear concentration-dependent property. A-4166 at 0.3 mmol/L and tolbutamide at 3 mmol/L exhibited maximal stimulation of insulin release to a similar extent, indicating that A-4166 is one log-order more potent than and as effective as tolbutamide. By contrast, A-4166 stimulated somatostatin release to a threefold greater extent than tolbutamide. A-4166 evoked an increase in the cytosolic free-Ca2+ concentration ([Ca2+]i) in rat pancreatic beta cells. [Ca2+]i and insulin secretory responses to A-4166 were inhibited by nitrendipine (NTD), a blocker of the L-type Ca2+ channel, and by diazoxide (DAZ), an opener of the adenosine triphosphate (ATP)-sensitive K+ channel. Furthermore, A-4166-stimulated somatostatin release was also inhibited by NTD and by DAZ. The results indicate that A-4166 and tolbutamide stimulate the release of insulin and somatostatin, and that A-4166 is much more effective than tolbutamide in releasing somatostatin, a hormone that attenuates hyperglycemia under certain circumstances. It is concluded that A-4166-induced insulin release is mediated by an increase in [Ca2+]i in beta cells. An inhibition of ATP-sensitive K+ channels and a consequent activation of L-type Ca2+ channels appear to play a key role not only in insulin secretion from beta cells, but also in somatostatin secretion from delta cells in response to A-4166.

A new hypoglycemic agent, A-4166, inhibits ATP-sensitive potassium channels in rat pancreatic beta-cells

Effects of a new hypoglycemic drug, N-[trans-4-isopropylcyclohexy-carbonyl]-D-phenylalanine (A-4166), on membrane current were investigated using the patch-clamp technique in single pancreatic beta-cells isolated from rats. A-4166, at a concentration of 10 microM, depolarized membrane potential of beta-cells and evoked action potentials in the presence of 2.8 mM glucose. The single ATP-sensitive K+ channel (K-ATP channel) current recorded in cell-attached membrane patches was reversibly inhibited by A-4166 (> 0.1 microM) without a change in the single-channel conductance of the K-ATP channel. Both A-4166 and tolbutamide inhibited the whole cell K-ATP channel current with half-maximum inhibition (IC50) of 0.23 and 12.8 microM, respectively (Hill coefficient = 1). In inside-out membrane patches, the IC50 with A-4166 occurred at 4.5 nM, in contrast to 0.7 microM for tolbutamide. A-4166 did not affect L- and T-type Ca2+ channels or the time-dependent outward current. We conclude that A-4166 specifically blocks the K-ATP channel and that the blockade is more potent than that of tolbutamide. The action of A-4166 underlies the mechanism by which the drug stimulates insulin secretion from beta-cells.

Possible role of the sympathetic nervous system in responses to interleukin-1

Interleukin-1 (IL-1) is a key mediator of changes in immune, endocrine and metabolic activities, collectively called the acute phase response, seen during infection and tissue injury. The purpose of the present study was to clarify a possible role of the sympathetic nervous system in the responses to IL-1 in rats. Intraperitoneal injection of IL-1 elicited an increase in rectal temperature and white blood cell count and a decrease in the plasma levels of glucose, iron and triglyceride. Pretreatment of rats with 6-hydroxydopamine or a ganglionic blocking agent abolished some of the responses, such as hypoglycemia and the increased white blood cell count. IL-1 injection also accelerated norepinephrine turnover, an index of sympathetic nerve activity, in the spleen and lung without appreciably affecting many other organs, such as the liver, heart, pancreas and brown adipose tissue. It was concluded that IL-1 activates the sympathetic nerves specifically in the spleen and lung, and can thereby influence the immune and metabolic functions of these organs.

Interleukin-1 increases norepinephrine turnover in the spleen and lung in rats

To clarify effects of interleukin-1 on sympathetic nerve activity, norepinephrine turnover in various organs was assessed in rats after intraperitoneal injection of recombinant human interleukin-1 beta. Interleukin-1 administration increased norepinephrine turnover in the spleen, lung and hypothalamus without appreciable effect in the heart, liver, submandibular gland, thymus, pancreas, brown adipose tissue and medulla oblongata. Similar changes in norepinephrine turnover were also found after the administration of bacterial endotoxin. It was concluded that interleukin-1 activates the sympathetic nerves specifically in the spleen and lung.

Ototoxic effects of a pseudodisaccharide aminoglycoside antibiotic, dactimicin, on the inner ears of guinea pigs

The effect of dactimicin on the inner ear of guinea pigs was investigated by comparing it with the effects of ribostamycin, astromicin and amikacin. At doses of 200 and 400 mg/kg/day for 4 weeks, no pinna reflex loss was observed, but 2 animals receiving 400 mg dactimicin/kg/day showed unilateral loss of the outer hair cells in the cochlea and very scattered loss of the hair cells in the vestibular organ. At doses of 400 and 500 mg dactimicin/kg/day for 5 weeks, all surviving animals showed no abnormality of the outer hair cells, the inner hair cells and the spiral ganglion cells in the cochlea except for scattered unilateral loss of the outer hair cells and loss of the stria vascularis. Based on these observations, it is concluded that the ototoxicity of dactimicin on the inner ear of guinea pigs is the same as or a little stronger than that of ribostamycin, weaker than or the same as that of astromicin and weaker than amikacin.

[Evaluation of ototoxic effect of micronomicin by intravenous drip infusion]

Ototoxic effect of micronomicin (MCR) in intravenous drip administration was investigated in guinea pigs (300--400 g) receiving MCR for 30 days at dose of 50 and 100 mg/kg, respectively. MCR was dissolved in physiologic saline and 1.5 ml of the solution was infused through polyethylene tube into the left external jugular vein with Perista mini-pump for 60 minutes every day after measurement of body weight. Auditory impairment was monitored by pinna reflex audiometry. Pinna reflex loss was not detected in any animal in frequency range (0.5 to 20 kHz). Cochlear hair cell damage generally was of mild degree. Two out of 6 animals treated with MCR 50 mg/kg (Table 1) showed outer hair cell loss confined to unilateral basal end and posterior 3/4 of the first turn, respectively. Outer hair cell loss was noticed in 4 of 9 animals receiving MCR 100 mg/kg (Table 2); much less extensive in 3 animals, unsymmetrical slightly extensive in remaining 1. Unilateral circumscribed loss of inner hair cells was noticed at lower part of the hook in the latter one. Vestibular hair cell loss was scattered and less extensive and occurred in 4 of the 6 50 mg/kg given animals and in 7 of the 9 100 mg/kg ones. Comparison in incidence and extension of the outer hair cell loss of the cochlea (Tables 3, 4) in the present study and previous ones on the ototoxic effect of MCR in intramuscular and intravenous administration suggests that there was no distinct difference in enhancement of the ototoxic effect in the intravenous drip administration.

[Effect of intravenous administration of micronomicin on the inner ear of guinea pigs]

The present experiment was made to clarify the effect of intravenous administration of micronomicin (sagamicin, MCR) on the inner ear of guinea pigs (300--350 g). MCR was given to the animals intravenously at dose of 25, 50 mg/kg and 100 mg/kg, respectively for 28 days. Pinna reflex test in frequency range from 20 kHz to 0.5 kHz was performed before, during and after the administration. The temporal bones were removed after intravital perfusion of the inner ears with neutral formation after the end of the administration. Histopathological examination was performed on the serial celloidin sections of the inner ears which had been stained with hematoxylin eosin. The following results were obtained. 1. MCR had a mild corti toxicity, which did not show remarkable dose dependent increase. 2. MCR had more affinity for the vestibular organs than for the organ of corti. The affinity for the vestibular organ increased with increase in dose. 3. MCR showed less increase in corti toxicity in intravenous administration than in intramuscular injection. However, the affinity of MCR for the vestibular organ showed little more increase in the intravenous administration than in the intramuscular injection.

[Ototoxicity study of netilmicin in pregnant guinea pigs and the embryo]

The ototoxicity of netilmicin (NTL) in pregnant guinea pigs (Hartley strain) and the newborn was examined and compared to that of gentamicin (GM). NTL was administered intramuscularly at dose of 90 mg/kg to pregnant guinea pigs from day 0 to day 35 of pregnancy (the early period of pregnancy) or from day 42 of pregnancy to 1 day prior to delivery (the late period of pregnancy). GM at dose of 45 mg/kg or physiological saline were administered intramuscularly to pregnant guinea pigs during the late period of pregnancy. Four of 5 dams given NTL during the early period of pregnancy, 4 of 7 dams given TNL during the late period of pregnancy, and 2 of 4 dams given GM during the late period of pregnancy died. No pinna reflex loss in frequency range from 2 to 20 KHz were detected in mother guinea pigs treated with NTL either during the early period of pregnancy or during the late period of pregnancy. GM caused a loss of pinna reflex at 20 KHz in mother guinea pigs treated during the late period of pregnancy. Histopathologically, no damages were detected in the cochlea of mother guinea pigs treated with NTL during the early or late period of pregnancy, whereas slight scattered loss of hair cells was seen in the vestibulum. However, GM at dose of 45 mg/kg, caused an incomplete scattered loss of outer hair cells in the spiral organ, moderate atrophy of the spiral ganglion cells and a partial loss of hair cells in the vestibular organs in mother guinea pigs treated during the late period of pregnancy. In newborn guinea pig from the pregnant one treated with NTL during the early period of pregnancy, there was no loss of pinna reflex. The same results were obtained in newborn guinea pigs from the pregnant ones treated with either NTL or GM during the late period of pregnancy. No histopathological damages were detected. The present study suggests that NTL has a minimal effect on the auditory and vestibular organs in pregnant guinea pigs and the newborn and is considered to be 1 of the aminoglycosides with low ototoxic potential.

[Animal test for evaluation of ototoxicity and safety of KW-1062 (author's transl)]

KW-1062, a new aminoglycoside antibiotic, was tested for the evaluation of audiotoxicity in administration at higher dosage and compared with the audiotoxicity of gentamicin. KW-1062 was given at dosage of 50, 100 and 150 mg/kg intramuscularly for 4 weeks to each group consisting of 10 healthy guinea pigs, respectively. Gentamicin was administered at dosage of 25, 35, 50 and 100 mg/kg in the same way as in KW-1062 to the guinea pigs. In the present study the differential frequency pinna reflex test in the frequency range from 20 kHz to 0.5 kHz was performed before and during administration of the drugs, to evaluate the audiotoxicity. Comparison of number of animal with pinna reflex loss and extent of frequency range of pinna reflex loss revealed that KW-1062 at dose of 150 mg/kg is less audiotoxic than gentamicin at 50 mg/kg and 100 mg/kg, and approximately equivalent in audiotoxicity to gentamicin at dose of 35 mg/kg.

Audiotoxicosis in newborn guinea pigs from pregnant ones given sisomicin

The audiotoxic effect of sisomicin was investigated in guinea pig injected intramuscularly with 6.25, 12.5, 25 and 50 mg/kg of sisomicin sulfate (potential) during weeks 1--5 or 5--9 of pregnancy, and the transplacental effect on their offspring was studied. While, in some dams the higher doses of sisomicin produced a limited effect on the pinna reflex and the outer hair cells of the organ of Corti, no such effects were noted in any of the offspring during the 3-week postnatal observation period.

[Ototoxic effect of BB-K8 administered to pregnant guinea pigs on development of inner ear of intrauterine litters (author's transl)]

Transplacental ototoxic effects of BB-K8 on development of inner ear in intrauterine guinea pigs were evaluated by differential frequency pinna reflex test in range of 20 kHZ to 500 HZ and histopathological examination of spiral and vestibular organs in new born guinea pigs from pregnant ones given BB-K8 i.m. during gestation.

MATERIALS AND METHODS

Twenty-five pregnant guinea pigs of the Hartley strain and 63 new-born guinea pigs from the pregnant ones were used in the study. Following antibiotics were given i.m. daily to the 20 pregnant guinea pigs from 7th day of gestation for 56 days. BB-K8 was given at the dose level of 100 mg/kg and 200 mg/kg, respectively. Kanamycin (KM) was administered at the dose level of 100 mg/kg and 200 mg/kg, respectively. Physiological saline solution (1.0 ml/kg) was given i.m. to the pregnant guinea pigs for 56 days. The differential frequency pinna reflex test was performed in the frequency range from 20 kHZ to 500 HZ to determine an extent of frequency of pinna reflex loss. The test was carried out before the start of administration of the antibiotics and once a week during the administration. After the last injection of the antibiotics, intravital perfusion fixation was carried out in the new born animals under anesthesia with nembutal. Histopathological examination was made in celloidin serial sections of the cochlea and vestibulum of the new born animals to observe an extent or degree of hair cell damage.

RESULTS

(1) The differential frequency pinna reflex test revealed that new born guinea pigs from the pregnant ones given BB-K8 and KM respectively at the dose level of 100 mg/kg did not show occurrence of pinna reflex loss at any frequency tested. At the dose level of 200 mg/kg, BB-K8 did not result in transplacental hearing impairment in new born guinea pigs, but KM caused transplacental pinna reflex loss in the highest frequencies from 20 k to 15 kHZ in 3 of 10 animals. (2) Histopathological examination detected that unilateral incomplete loss of outer hair cells of the spiral organ confined to the basal end of cochlea was found in 3 of 13 new born guinea pigs from the pregnant ones treated with BB-K8 (100 mg/kg). In the animals, slight damage of hair cells in the vestibular organs occurred in 100%. These hair cell damages were enhanced slightly in the new born guinea pigs from the pregnant ones treated with BB-K8 (200 mg/kg) and much more in the new born ones from the pregnant ones treated with KM (100 mg/kg, 200 mg/kg). (3) These results suggest that BB-K8 has a mild potency to cause transplacental ototoxic damage in the inner ear of intrauterine guinea pigs within the pregnant ones treated for 56 days (normal gestation period approximately 70 days).

[Ototoxicity of spectinomycin (author's transl)]

Spectinomycin is an aminocyclitol antibiotic, but different in chemical structure from other aminocyclitol antibiotics such as streptomycin, kanamycin and gentamicin. Spectinomycin clinically has been proven to be highly effective in the intramuscular single-dose treatment of gonorrhea. According to NOVAK et al. (1974), all evidence from pharmacological and clinical efficacy studies to date indicates that spectinomycin is free from ototoxic effects at the dose levels recommended for single-dose treatment of gonorrhea (2 or 4 g) or repeated i.m. or i.v. doses, 8g/day. The present experimental study has been made to evaluate the ontoxocic effects of spectinomycin in Hartley strain guinea pigs given i.m. a single-high dose (800 mg/kg or 1,600 mg/kg) and repeated-slightly higher dose (80 mg/kg or 160 mg/kg daily for 4 weeks) respectively. Differential frequency pinna reflex test in frequency range from 20 KHz to 500 Hz revealed that no animals showed disappearance of pinna reflex in the frequencies tested. Histologic examination in serial celloidin sections of the cochlea and vestibulum disclosed that a few animals given a single-high dose of spectinomycin (800 mg/kg or 1,600 mg/kg) and repeated-slightly higher dose or spectinomycin (80 mg/kg daily for 4 weeks) respectively showed limited mild damage of outer hair cells in the spiral organ and of hair cells in the vestibular organ. There were histologically a few focal necrosis in the liver and scattered interstitial cell infiltration around the proximal convoluted tubules which are lined with regenerated epithelial cells in some animals given the single-high dose (800 mg/kg or 1,600 mg/kg) or repeated-slightly higher dose (80 mg/kg or 160 mg/kg daily for 4 weeks) of spectinomycin. Positive correlation between the extent of the hair cell damage and the injury of the liver and kidney was not confirmed. The present study suggests that administration of spectinomycin at the dose levels recommended for single-dose treatment of gonorrhea (2 or 4 g) most probably is free from ototoxic effect.