Estimation of Photon Path Length and Penetration Depth in Articular Cartilage Zonal Architecture over the Therapeutic Window.

OBJECTIVE: The key characteristics of light propagation are the average penetration depth, average maximum penetration depth, and average path length of photons. These parameters depend on tissue optical properties and, thus, on the pathological state of the tissue. Hence, they could provide diagnostic information on tissue integrity. This study investigates these parameters for articular cartilage which has a complex structure. METHODS: We utilize Monte Carlo simulation to simulate photon trajectories in articular cartilage and estimate the average values of the light propagation parameters (penetration depth, maximum penetration depth, maximum lateral spread, and path length) in the spectral band of 400-1400 nm based on the optical properties of articular cartilage zonal layers and bulk tissue. RESULTS: Our findings suggest that photons in the visible band probe a localized small volume of articular cartilage superficial and middle zones, while those in the NIR band penetrate deeper into the tissue and have larger lateral spread. In addition, we demonstrate that a simple model of articular cartilage tissue, based on the optical properties of the bulk tissue, is capable to provide an accurate description of the light-tissue interaction in articular cartilage. CONCLUSION: The results indicate that as the photons in the spectral band of 400-1400 nm can reach the full depth of articular cartilage matrix, they can provide viable information on its pathological state. Therefore, diffuse optical spectroscopy holds significant importance for objectively assessing articular cartilage health. SIGNIFICANCE: In this study, for the first time, we estimate the light propagation parameters in articular cartilage.

Receptor binding and biological activity of the dermorphin analog Tyr-D-Arg(2)-Phe-Sar (TAPS).

The binding of Tyr-D-Arg(2)-Phe-sarcosine(Sar)(4) (TAPS), a proposed mu-opioid receptor-selective tetrapeptide analog of dermorphin to opioid receptors, was studied using selective binding assays for subtypes of mu-, delta- and kappa-opioid receptors. Subtype specific mu-opioid receptor binding was further characterized in the presence of sodium and guanosine nucleotides and the activity of TAPS in isolated guinea pig ileum was compared to other mu-opioid receptor-selective ligands. Further, the antinociceptive properties of TAPS following intrathecal (i.t.) administration in rats, as a model of spinal antinociception, were evaluated. The K(i)-values for TAPS at the mu(1)- and mu(2)-opioid receptor sites were 0.4 and 1.3 nM, respectively, suggesting high affinity binding to mu-opioid receptor binding sites with an increased selectivity to mu(1)-opioid receptor sites. The attenuated reduction of TAPS binding at the mu(2)-opioid receptor subtype in the presence of the stable guanosintriphosphate analog 5'-guanylylimidodiphosphate and sodium suggests a potential partial antagonist mode of action at this site.

Dermorphin analog Tyr-D-Arg2-Phe-sarcosine-induced opioid analgesia and respiratory stimulation: the role of mu 1-receptors?

Tyr-D-Arg2-Phe-sarcosine4 (TAPS), a mu-selective tetrapeptide analog of dermorphin, induced sustained antinociception and stimulated ventilatory minute volume (MV) at the doses of 3 to 100 pmol i.c.v. The doses of 30 and 100 pmol i.c.v. induced catalepsy. The effect of TAPS on MV was in negative correlation with the dose and the maximal response was achieved by the lowest (3 pmol) dose (+63 +/- 23%, P < .05). Morphine, an agonist at both mu 1 and mu 2 sites, at a dose of 150 nmol i.c.v. (equianalgesic to 100 pmol of TAPS decreased the MV by 30%, due to a decrease in ventilatory tidal volume. The antinociceptive effect of TAPS was antagonized by naloxone and the mu 1 receptor antagonist, naloxonazine. Naloxonazine also attenuated the catalepsy produced by 100 pmol of TAPS i.c.v. and the respiratory stimulation produced by 3 pmol of TAPS i.c.v. Pretreatment with 30 pmol of TAPS antagonized the respiratory depression induced by the mu opioid agonist dermorphin (changes in MV after dermorphin alone at 1 or 3 nmol were -22 +/- 10% and -60 +/- 9% and, after pretreatment with TAPS, +44 +/- 11% and -18 +/- 5%, respectively). After combined pretreatment with naloxonazine and TAPS, 1 nmol of dermorphin had no significant effect on ventilation. In contrast, pretreatment with a low respiratory stimulant dose (10 pmol i.c.v.) of dermorphin did not modify the effect of 1 nmol of dermorphin. In conclusion, the antinociceptive, cataleptic and respiratory stimulant effects of TAPS appear to be a related to its agonist action at the mu 1 opioid receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Respiratory mu-opioid and benzodiazepine interactions in the unrestrained rat.

Interactions of mu-opioid receptors with the benzodiazepine system were studied by examining the modulatory effects of flumazenil (a benzodiazepine antagonist) and alprazolam (a benzodiazepine agonist) on the respiratory effects of the opioid peptide dermorphin. Dermorphin, 1-30 nmol administered i.c.v., to conscious, unrestrained rats decreased ventilation rate (VR) and minute volume (MV) dose-dependently. The ventilatory depression was antagonized by naloxone and by the benzodiazepine antagonist flumazenil. The benzodiazepine alprazolam potentiated the respiratory inhibition of a small (1 nmol) dose of dermorphin but antagonized that of a higher dose (3 nmol). The results suggest that the benzodiazepine/GABA receptor complex modulates respiratory depression induced by central mu-receptor stimulation in the rat.

Evidence for differential opioid mu 1- and mu 2-receptor-mediated regulation of heart rate in the conscious rat.

The possibility that mu-opioid-induced tachycardia and bradycardia could be mediated by different subtypes of the mu-receptor was studied in conscious Sprague-Dawley rats. The selective mu-receptor agonist dermorphin and its analog, TAPS (Tyr-D-Arg-Phe-sarcosine), a putative mu 1-receptor agonist, were given centrally. Tyr-D-Arg-Phe-sarcosine increased the heart rate, the response being inversely correlated to the dose (an increase of 71 +/- 22, 49 +/- 14 and 30 +/- 17 beats/min at doses of 0.3, 3 and 30 pmol, respectively). Dermorphin induced less clear changes in heart rate (maximum increase of 39 +/- 14 beats/min at the dose of 1 pmol). After treatment with the mu 1-selective antagonist naloxonazine (NAZ), TAPS 30 pmol and dermorphin 1 pmol decreased heart rate by -22 +/- 10 and -24 +/- 7 bpm, respectively. The bradycardiac effect of larger doses of dermorphin was potentiated by NAZ (from -25 +/- 8 to -97 +/- 22 bpm) but abolished by the non-selective antagonist naloxone. These data suggest that the high affinity mu 1-opioid receptors mediate tachycardic responses and mu 2-receptors mediate bradycardic responses.

Respiratory and locomotor stimulation by low doses of dermorphin, a mu1 receptor-mediated effect.

The selective opioid mu receptor agonist dermorphin increased the locomotor activity of rats dose dependently at 10 to 100 pmol/kg i.c.v. Respiratory rate, relative tidal volume and respiratory minute volume also increased unrelated to changes in locomotor activity. Higher doses, on the other hand, produced catalepsy and respiratory depression. Pretreatment of the rats with the mu1-selective antagonist naloxonazine (10 mg/kg i.v.) blocked the stimulant locomotor and respiratory effects of low doses of dermorphin (10-100 pmol/kg), but potentiated the respiratory depressant effect of a high dose (10 nmol/kg) of dermorphin. The selective benzodiazepine antagonist flumazenil (5 mg/kg), which has been shown previously to antagonize catalepsy and respiratory depression produced by relatively high doses of dermorphin, did not antagonize the respiratory or locomotor stimulant effect of dermorphin. The data suggest that mu1-opioid receptors are responsible for the low dose stimulant effects of dermorphin on locomotor activity and respiration whereas mu2 receptors mediate the respiratory depressant effect of dermorphin.

Mechanisms of central hemodynamic and sympathetic regulation by mu opioid receptors: effects of dermorphin in the conscious rat.

The effects of i.c.v. administered dermorphin, a highly selective mu-opioid agonist, on cardiac function and renal, mesenteric and hindquarter blood flow were studied in conscious rats. Core temperature, blood gases, arterial plasma levels of norepinephrine, epinephrine, dopamine, 3,4-dihydroxyphenylalanine and dihydroxyphenylacetic acid (DOPAC) also were examined. Cardiac output was measured using a thermodilution technique and regional blood flows using directional pulsed Doppler velocimetry. Dermorphin, at doses of 0.1-100 nmol/kg, increased blood pressure and hindquarter blood flow, renal and mesenteric resistance, and core temperature. Higher doses (1-5 mumol/kg) caused respiratory depression, acidosis, and shock despite profound sympatho-adrenomedullary stimulation. Circulating levels of catecholamines were significantly increased at the dermorphin doses of 0.1-100 nmol/kg. At the 100 nmol/kg dose, plasma levels of epinephrine, norepinephrine, the dopamine metabolite dihydroxyphenylacetic acid and the catecholamine precursor 3,4-dihydroxyphenylalanine were increased by 2-15-fold. The data indicate that mu opioid receptor stimulation exerts potent effects on cardiorespiratory functions, activates the sympathoadrenomedullary system and produces a pattern of blood flow changes consistent with the stress-induced "defense" response (skeletal muscle vasodilation and splanchnic vasoconstriction). Excessive mu opioid receptor stimulation leads to shock due to respiratory and hemodynamic collapse.

Antagonism of dermorphin-induced catalepsy with naloxone, TRH-analog CG3703 and the benzodiazepine antagonist, Ro 15-1788.

Intracerebroventricular (i.c.v.) administration of the highly selective opiate mu-receptor agonist, dermorphin, produced dose-dependent catalepsy in conscious rats. The cataleptic effect of dermorphin was abolished by pretreatment (intraperitoneal, i.p.) with the opiate-antagonist naloxone (5 mg/kg), thyrotropin-releasing hormone analog CG3703 (1 mg/kg) or the benzodiazepine-antagonist Ro 15-1788 (5 mg/kg) whereas pretreatment with the benzodiazepine alprazolam (1 mg/kg) potentiated the cataleptic effect of dermorphin. When given to cataleptic rats, naloxone and CG3703, but not Ro 15-1788, reversed the dermorphin-induced catalepsy. The data suggest an involvement of benzodiazepine receptors in the induction of catalepsy mediated by opioid mu-receptors. Other opioid-modulating neuronal systems, antagonized by CG3703, may be involved in maintaining the dermorphin-induced cataleptic state.

Effect of neuromuscular blocking drugs on arterial pressure and heart rate in rats.

The effects of neuromuscular blocking drugs on mean arterial pressure (MAP) and heart rate (HR) were studied in rats which were anaesthetised, tracheotomized and ventilated artificially. The arterial pressure was recorded from the carotid artery. Seven neuromuscular blocking drugs were injected intravenously at doses of 1, 5, and 25 mumol/kg. d-Tubocurarine, alcuronium and vecuronium lowered MAP in a dose dependent manner (maximum 40%). Succinylcholine, 1 mumol/kg, reduced MAP and HR, whereas the two larger doses increased them. Gallamine, 25 mumol/kg, or metocurine and pancuronium, 1 or 5 mumol/kg, each, induced short-lasting rises in MAP. Pancuronium, 25 mumol/kg, decreased MAP by 25%, while the largest dose of metocurine appeared to be toxic. The cardiovascular responses to neuromuscular blocking drugs were antagonized or abolished by pretreatment with the ganglionic blocking agent pentolinium. Pentolinium itself markedly reduced MAP and HR. After ganglionic blockade and restoration of MAP by noradrenaline infusion, all the neuromuscular blocking drugs induced short-lasting increases in MAP (10-30%), except d-tubocurarine which still reduced MAP by 30%, a fall which, in contrast to the effect in the absence of the pretreatments, was transient. This response to d-tubocurarine could not be abolished by a combined pretreatment with H1 and H2 antagonists showing that the hypotensive effect of this drug was not due to the liberation of histamine. These results suggest that the cardiovascular responses to neuromuscular blocking drugs in rats might be partly due to ganglionic effects. Other mechanisms are also involved since after the restoration of blood pressure by noradrenaline during the ganglionic blockade some cardiovascular responses to these drugs still occurred.

Cardiovascular and ventilatory effects of taurine and homotaurine in anaesthetized rats.

The cardiovascular and ventilatory effects of intravenous (i.v.) or intracerebroventricular (i.c.v.) injections of the aminosulphonic acids, taurine and homotaurine, were studied in urethane-anaesthetized rats. Taurine induced dose-dependent falls in blood pressure, heart rate and ventilatory tidal volume on i.c.v. but not on i.v. administration. Homotaurine induced dose-dependent hypotension and bradycardia when given i.v. and i.c.v. It was, however, more effective when injected i.c.v., and the decrease in ventilatory tidal volume occurred after i.c.v. administration of homotaurine only. Pretreatment of the rats with reserpine attenuated both the hypotensive and bradycardic responses to taurine and homotaurine. Atenolol and atropine both partly inhibited, and in combination totally abolished, the bradycardic effects of taurine and homotaurine without changing the hypotensive responses to these compounds. The ventilatory responses were not significantly changed by any of the pretreatments. The results suggest that the central cardiovascular effects of taurine and homotaurine are mediated both by a decrease in sympathetic tone and an increase in the parasympathetic tone.

Peripheral hypotensive and central hypertensive effects of cimetidine.

Rapid intravenous (i.v.) injections of high doses (16-128 mumol/kg) of cimetidine induced a short-lasting (5-15 min) hypotension in anaesthetized rats. Diastolic pressure was reduced more than systolic pressure, suggesting vasodilatation. Heart rate was not affected. Diphenhydramine pretreatment (100 mumol/kg i.v.) did not antagonize the hypotensive effect of cimetidine. However, in the presence of diphenhydramine, cimetidine induced bradycardia. Intracerebroventricular administration of cimetidine or metiamide (2 mumol/rat) increased the blood pressure and heart rate. It is concluded that the hypotension after i.v. cimetidine is mediated by peripheral mechanisms. Since diphenhydramine pretreatment had no antagonistic effect cimetidine-induced hypotension could not be due to indirect H1-receptor stimulation caused by histamine liberation.

Further evidence for central histamine H2-receptor involvement in the hypotensive effect of clonidine in the rat.

In urethane-anaesthetised rats, the administration of the specific histamine H2-receptor antagonist metiamide intracerebroventricularly (i.c.v.) raised the blood pressure and increased the heart rate. Metiamide (i.c.v.) antagonised the hypotensive effect of clonidine (i.c.v.) in an apparently competitive manner. 4-Methylhistamine i.c.v. did not significantly change the blood pressure. The results are consistent with the concept that the hypotensive effect of clonidine is at least partly due to a stimulation of cerebral H2-receptors. The existence of cerebral H2-receptors mediating hypotensive effects is supported by the hypertensive effect of metiamide but not by the lack of hypotensive effects of 4-methylhistamine.

Central hypotensive effects of angiotensin II in the rat.

The floor of the fourth cerebral ventricle of urethane-anesthetized rats was exposed through the occipital foramen. Angiotensin II (10-1000 ng), applied onto the surface of the area postrema, induced a rapid lowering of the blood pressure. Pretreatment of the rats with reserpine abolished the hypotensive response to angiotensin II. It is concluded that the local application of angiotensin II induced in the vicinity of the area postrema a release of some biogenic amine, which has an inhibitory effect on the cardiovascular centres.

Site and mode of action of clonidine in the central nervous system.

In urethane-anaesthetized rats clonidine was administered intravenously (i.v.), intracerebroventricularly (i.c.v.) or onto the surface of the area postrema which protrudes into the fourth cerebral ventricle. In each instance clonidine induced a dose-dependent lowering of the blood pressure. The region of the area postrema appears to be the most sensitive site for the action of clonidine so far studied. In order to obtain similar blood pressure effects, approximately 8 times higher amounts were needed i.c.v., and about 80 times higher amounts i.v., than onto the surface of the area postrema. A pretreatment of the rats with the specific histamine H2-receptor blocking drug, metiamide (4.5 micronmoles/rat i.c.v.) shifted the dose-response curve of clonidine (i.c.v.) to the right. The results suggest that clonidine exerts its hypotensive effect in the rat via a stimulation of histamine H2-receptors in, or in the vicinity of, the area postrema.