Biomedical subjects

T M Mills

Publications and source records attributed to T M Mills.

At least 19 recordsLinked to original sources

PubMed2005

Rho-kinase and RGS-containing RhoGEFs as molecular targets for the treatment of erectile dysfunction.

Erectile dysfunction (ED) is a highly prevalent and often under-treated condition. Erection is basically a spinal reflex that can be initiated by recruitment of penile afferents but also by visual, olfactory and imaginary stimuli. The generated nervous signals will influence the balance between contractile and relaxant factors, which control the degree of contraction of penile corporal cavernosal smooth muscles and, thus, determine the erectile state of the penis. The different steps involved in neurotransmission, impulse propagation and intracellular transduction of neural signals may be changed in different types of ED. Recent studies have revealed important roles for the small GTPase RhoA and its effector, Rho-kinase in regulating cavernosal smooth muscle tone. The RhoA/Rho-kinase pathway modulates the level of phosphorylation of the myosin light chain, mainly through inhibition of myosin phosphatase, and contributes to agonist-induced Ca(2+)-sensitization in smooth muscle contraction. Changes in this pathway may contribute to ED in various patient subgroups (e.g. hypertension, diabetes, hypogonadism). This review summarizes the importance of Rho-kinase signaling in the erectile response and introduces the evidence pointing to RGS-containing Rho-guanine nucleotide exchange factors (GEFs) as critical mediators of RhoA-GTPase activation in cavernosal smooth muscle and its possible compartmentalization in the caveolae. In addition, we suggest that the design of selective inhibitors of these GEFs might represent a novel class of pharmacological agents to treat ED.

Animals↗

PubMed2004

Topical application of a Rho-kinase inhibitor in rats causes penile erection.

Studies from this laboratory have demonstrated that RhoA/Rho-kinase signaling mediates vasoconstriction in the penile circulation of the rat and that erection results from inhibition of this activity with Y-27632. In prior animal studies, Y-27632 was administered to the rats by intracavernous injection. To determine if topical application of the Rho-kinase inhibitor is an effective mode of delivery, Y-27632 was applied to the surface of the tunica albuginea or to the glans penis and surrounding skin in intact or castrated rats. Both sites of drug administration resulted in a marked increase in the erectile response both with and without stimulation of the autonomic innervation of the penile vasculature. Although high doses of the drug were found to reduce systemic blood pressure, topical administration of the Rho-kinase inhibitor, in appropriate doses, may have clinical value for the treatment erectile dysfunction.

Administration, Topical↗

PubMed2003

The ups and downs of Rho-kinase and penile erection: upstream regulators and downstream substrates of rho-kinase and their potential role in the erectile response.

In the absence of arousal stimuli, the activity of the Rho-kinase-mediated signaling pathway promotes vasoconstriction of the cavernosal arterioles and sinuses, keeping the penis in the nonerect state. Upon sexual arousal or during nocturnal tumescence, nitric oxide (NO), released from nonadrenergic/noncholinergic nerves or from local endothelial cells, induces cavernosal vasodilation, resulting in an elevation in blood flow and intracavernosal pressure to initiate the erectile response. Although NO is thought to be the principal stimulator of penile erection, the signaling mechanism(s) of NO-mediated cavernosal vasodilation is unknown. In this article, we will consider the novel hypothesis that NO induces penile erection through the inhibition of endogenous Rho-kinase-mediated vasoconstriction. Additionally, we will look downstream of Rho-kinase, introducing a potential role for various substrates in the mechanism of Rho-kinase-mediated constriction in the cavernosal vasculature.

Animals↗

PubMed2003

Vasoconstriction, RhoA/Rho-kinase and the erectile response.

Recent studies have suggested that contraction of the smooth muscle in the cavernosal arterioles and in the walls of the cavernosal sinuses is maintained by the RhoA/Rho-kinase signaling pathway. However, this contraction activity must be overcome to permit the vasorelaxation essential for erection. We postulate that nitric oxide (NO) causes erection primarily by inhibiting the RhoA/Rho-kinase pathway. The following will discuss evidence in support of the important role of Rho-kinase-mediated vasoconstriction in the nonerect penis and how NO overrides this Rho-kinase-mediated vasoconstriction to permit vasodilation and erection.

Humans↗

PubMed2003

The human sexuality education of physicians in North American medical schools.

Individuals seeking treatment for sexual problems frequently would like to turn to a source they consider knowledgeable and worthy of respect, their doctor. The objective was to assess how well the 125 schools of medicine in the United States and the 16 in Canada prepare physicians to diagnose and treat sexual problems. A prospective cohort study was carried out. The main outcome results were description of the medical educational experiences, teaching time, specific subject areas, clinical programs, clerkships, continuing education programs in the domain of human sexuality in North American medical schools. The results were as follows. There were 101 survey responses (71.6%) of a potential of 141 medical schools (74% of United States and 50% of Canadian medical schools). A total of 84 respondents (83.2%) for sexuality education used a lecture format. A single discipline was responsible for this teaching in 32 (31.7%) schools, but a multidisciplinary team was responsible in 64 (63.4%) schools (five schools failed to respond to the question). The majority (54.1%) of the schools provided 3-10 h of education. Causes of sexual dysfunction (94.1%), its treatment (85.2%) altered sexual identification (79.2%) and issues of sexuality in illness or disability (69.3%) were included in the curriculum of 96 respondents. Only 43 (42.6%) schools offered clinical programs, which included a focus on treating patients with sexual problems and dysfunctions, and 56 (55.5%) provided the students in their clerkships with supervision in dealing with sexual issues. In conclusion, expansion of human sexuality education in medical schools may be necessary to meet the public demand of an informed health provider.

Canada↗

PubMed2002

Captopril treatment reverses erectile dysfunction in male stroke prone spontaneously hypertensive rats.

The involvement of antihypertensive therapy in the pathology of hypertension associated male erectile dysfunction is unclear. Stroke prone spontaneously hypertensive rats (SHRSP) were treated chronically with the angiotensin converting enzyme (ACE) inhibitor captopril or placebo, normotensive rats served as controls. Mean arterial and intracavernosal pressure were measured during the induction of erection by autonomic ganglion stimulation. SHRSP-placebo treated rats were hypertensive and had a blunted erectile response. Captopril treatment returned both the blood pressure and erectile response to control levels. Therefore, ACE inhibitor therapy may not be responsible for the erectile dysfunction observed in treated hypertensive subjects.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2001

New biochemical pathway may control erection.

Thirty million men in the U.S. suffer from erectile dysfunction (ED) defined by their inability to achieve or maintain a penile erection sufficient for intercourse. An unestimated number of women also suffer from sexual dysfunction resulting from many of the same causes that lead to ED in men. There are a variety of treatments available for ED including intracavernosal injection, transurethral therapy, surgery, vacuum therapy, and oral medication. Unfortunately, not all patients benefit from these currently available forms of therapy, and side effects are not uncommon. Sildenafil (Viagra) has been a highly successful drug for the treatment of ED but it does not work in all men . Some may experience a variety of side effects, and Viagra is contraindicated to some cardiac medications. These problems point to the need for new and different approaches to the treatment of sexual problems.

Animals↗

PubMed2001

Antagonism of Rho-kinase stimulates rat penile erection via a nitric oxide-independent pathway.

Relaxation of the smooth muscle cells in the cavernosal arterioles and sinuses results in increased blood flow into the penis, raising corpus cavernosum pressure to culminate in penile erection. Nitric oxide, released from non-adrenergic/non-cholinergic nerves, is considered the principle stimulator of cavernosal smooth muscle relaxation, however, the inhibition of vasoconstrictors (that is, norepinephrine and endothelin-1, refs. 5-9) cannot be ignored as a potential regulator of penile erection. The calcium-sensitizing rho-A/Rho-kinase pathway may play a synergistic role in cavernosal vasoconstriction to maintain penile flaccidity. Rho-kinase is known to inhibit myosin light chain phosphatase, and to directly phosphorylate myosin light-chain (in solution), altogether resulting in a net increase in activated myosin and the promotion of cellular contraction. Although Rho-kinase protein and mRNA have been detected in cavernosal tissue, the role of Rho-kinase in the regulation of cavernosal tone is unknown. Using pharmacologic antagonism (Y-27632, ref. 13, 18), we examined the role of Rho-kinase in cavernosal tone, based on the hypothesis that antagonism of Rho-kinase results in increased corpus cavernosum pressure, initiating the erectile response independently of nitric oxide. Our finding, that Rho-kinase antagonism stimulates rat penile erection independently of nitric oxide, introduces a potential alternate avenue for the treatment of erectile dysfunction.

Animals↗

PubMed2001

RhoA/Rho-kinase: a novel player in the regulation of penile erection.

Current research has centered around the role of nitric oxide in the stimulation of cavernosal vasodilation and erection. However, recent evidence from our lab details the importance of endogenous vasoconstrictor mechanisms in maintaining a flaccid penile state, and further demonstrates that the inhibition of endogenous vasoconstriction is sufficient to stimulate erection in a rat model. In this article, we suggest inhibition of endogenous vasoconstriction as a potential therapeutic avenue in the treatment of erectile dysfunction. We also speculate on potential physiologic mechanisms by which endogenous vasoconstriction is inhibited in order for arousal-initiated vasorelaxation, and erection, to occur.

Enzyme Inhibitors↗

PubMed2001

Erection and NO override the vasoconstrictive effect of alpha-adrenergic stimulation in the rat penile vasculature.

Studies in this laboratory are designed to determine the effects of vasoconstrictor agents on the erectile response in rats. We have previously demonstrated that the vasoconstrictor effect of endothelin-1 (ET-1) is sharply reduced by erection and by nitric oxide (NO) administration. The present study was performed to determine if vasoconstriction, resulting from alpha-adrenergic stimulation, is altered by erection and NO. During continuous monitoring of corpus cavernosum pressure (CCP) and mean arterial pressure (MAP), erection was induced by electrical stimulation of the autonomic ganglion for the innervation of the penis. When the alpha-adrenergic agonist methoxamine (METH, 10 microg/kg) was injected before erection (ie, into the non-erect penis), the subsequent erectile response (CCP/MAP) was significantly reduced from 0.68+/-0.03 before METH to 0.34+/-0.08 after METH. Injection of METH into the erect penis (ie, during erection) reduced the vasoconstrictor action of METH; CCP/MAP was 0.74+/-0.02 before METH and 0.55+/-0.05 after METH (P<0.05). The vasoconstrictor action of METH was slightly reduced when given in conjunction with NOR-1, a NO donor drug; CCP/MAP was 0.70+/-0.05 before METH, 0.55+/-0.09 after METH but this change was not significant. These results demonstrate that the response to alpha-adrenergic stimulation is attenuated during erection in response to ganglionic stimulation. Furthermore, it appears that NO, produced during erection, may serve to override agonist-induced vasoconstriction. These results support our hypothesis that NO acts to directly stimulate relaxation of cavernous smooth muscle and to inhibit the vasoconstrictor actions of agents like ET-1 and alpha-adrenergic agonists including norepinephrine.

Adrenergic alpha-Agonists↗

PubMed2001

Decreased penile erection in DOCA-salt and stroke prone-spontaneously hypertensive rats.

Numerous etiological studies have established a positive clinical association between hypertension and erectile dysfunction. However, to date, the mechanism underlying this dysfunction remains to be established. In this study, we demonstrate the presence of erectile dysfunction in two rat models of hypertension, and hypothesize that increased vasoconstrictor signaling via Rho-kinase contributes to the decreased erectile response. We found deoxycorticosterone-salt and stroke prone-spontaneously hypertensive rats to exhibit a decreased erectile response, recorded as intracavernosal pressure/mean arterial pressure (ICP/MAP) upon electrical stimulation of the major pelvic ganglion. As previously shown, inhibition of Rho-kinase activity by intracavernosal injection of the selective inhibitor, Y-27632, resulted in an increase in ICP/MAP. However, Y-27632 was significantly less effective at increasing ICP/MAP in the hypertensive as compared to normotensive rats. Additionally, intracavernosal injection of Y-27632 potentiated the voltage-stimulated increase in ICP/MAP in both hypertensive and normotensive rats, but was less effective at potentiating the voltage-mediated erectile response in the hypertensive rats. Altogether, our data demonstrate a decreased erectile response in a mineralocorticoid and genetic model of hypertension, and suggest the role of increased cell signaling by Rho-kinase in the vasoconstrictor activity of erectile dysfunction associated with hypertension.

Amides↗

PubMed2001

Vasoconstrictors in erectile physiology.

The erectile response of the penis depends on a balance between vasoconstrictor agents which cause cavernosal smooth muscle to contract limiting blood inflow, and vasodilators which relax cavernosal smooth muscle leading to increased blood inflow and erection. This review emphasizes the role of vasoconstrictors in the penis and shows that both endothelin-1 (ET-1) and the alpha-adrenergic agonist, methoxamine (METHOX) exert strong vasoconstrictor actions in the cavernosal circulation. We recently reported the vasoconstrictor actions of exogenous ET-1 and METHOX to be mediated by the RhoA/Rho-kinase pathway in the cavernosal circulation. While it is widely held that the nitric oxide-cyclic GMP-protein kinase G (NO-cGMP-PKG) pathway mediates vasorelaxation and penile erection, the interaction between this pathway and the vasoconstrictor process remains to be fully elucidated. Our studies also have shown that, during erection, the vasoconstrictor action of METHOX and ET-1 are inhibited and that NO is likely responsible for this inhibition. We hypothesize that the NO-cGMP-PKG pathway controls erection by acting in two distinct ways-by lowering intracellular levels of calcium leading to vasorelaxation and by inhibiting Rho-kinase mediated vasoconstriction.

Adrenergic alpha-Agonists↗

PubMed2001

Endothelin-1-induced vasoconstriction is inhibited during erection in rats.

Recent evidence indicates that endothelin-1 (ET-1) might be a principal vasoconstrictor in the penis. We report that ET-1 injection into the cavernous sinuses before erection sharply reduced the magnitude of subsequent erections. Corpus cavernosum pressure-to-mean arterial pressure ratios (CCP/MAP), with maximal ganglionic stimulation, were 0.62 +/- 0.05 before ET-1 injection and 0.31 +/- 0.05 after, indicating that ET-1 acted as a vasoconstrictor. When ET-1 was injected during a maximal neurally induced erection, the ability of ET-1 to attenuate subsequent erections was diminished (CCP/MAP 0.75 +/- 0.02 before ET-1, 0.61 +/- 0.03 after). At submaximal stimulation voltages, injection of ET-1 during erection also attenuated its vasoconstrictive effect. Similarly, when ET-1 was injected during erection induced by intracavernosal injection of the nitric oxide (NO) donor NOR-1, subsequent erections were not significantly suppressed (CCP/MAP 0.53 +/- 0.04 before ET-1, 0.45 +/- 0.04 after). These findings that ET-1-induced vasoconstriction is attenuated during erection are consistent with the hypothesis that NO mediates erection both by initiating pathways that cause smooth muscle relaxation and by inhibiting the vasoconstrictive actions of ET-1.

Animals↗

PubMed2001

Effect of Rho-kinase inhibition on vasoconstriction in the penile circulation.

A recent report from this laboratory (Chitaley K, Wingard C, Webb R, Branam H, Stopper V, Lewis R, and Mills T. Nature Medicine 7: 119-122, 2001) showed that inhibition of Rho-kinase increased the erectile response (intracavernosal pressure and mean arterial pressure) by a process that does not require nitric oxide or cGMP. The present study investigated whether vasoconstrictor agents, which are active in the penis, act via the Rho-kinase pathway. Western analysis revealed RhoA and Rho-kinase protein in the penis. Treatment with the selective Rho-kinase inhibitor Y-27632 significantly increased the magnitude of the erectile response. Intracavernous administration of endothelin-1 (ET-1; 50 pmol) or methoxamine (10 microg/kg) reduced the erectile response to autonomic stimulation. If Y-27632 was given before ET-1 or methoxamine, the vasoconstrictor effect was reduced, and intracavernosal pressure and mean arterial pressure remained elevated. However, when given after methoxamine, Y-27632 had a reduced vasodilatory effect, and Y-27632 had no vasodilatory effect when given after ET-1. These findings suggest that ET-1 and methoxamine increase Rho-kinase activity in the cavernous circulation and support the hypothesis that the vasoconstriction that maintains the penis in the nonerect state is mediated, in part, by the Rho-kinase pathway.

Amides↗

PubMed2001

Rho-kinase as a potential target for the treatment of erectile dysfunction.

Erectile dysfunction is a condition that is estimated to affect more than 30 million men in the United States alone. The prevalence of erectile dysfunction is increased with age and is often secondary to diseases such as depression, hypertension and diabetes. Causes of erectile dysfunction include physical injury to the cavernosum and abnormal cerebral and peripheral nervous system functioning. However, many cases of erectile dysfunction are the result of dysfunctional signaling in the cavernosal vasculature. This article will detail the important role of a vasoconstrictor mechanism mediated by the small G-protein RhoA and a downstream serine/threonine kinase, Rho-kinase, in the maintenance of penile flaccidity. Recent evidence demonstrates that inhibition of endogenous Rho-kinase initiates an erectile response in an in vivo rat model. These initial findings introduce a novel potential therapeutic approach for the treatment of erectile dysfunction.

Journal Article↗

PubMed2000

A single genetic determinant that prevents sex reversal in C57BL-YPOS congenic mice.

Sex determination in the mammalian embryo begins with the activation of a gene on the Y chromosome which triggers a cascade of events that lead to male development. The mechanism by which this gene, designated SRY in humans and Sry in mice (sex determining region of the Y chromosome), is activated remains unknown. Likewise, the downstream target genes for Sry remain unidentified at present. C57BL mice carrying a Y chromosome from Mus musculus musculus or molossinus develop normally as males. In contrast, C57BL/6 mice with the Y chromosome from M. m. domesticus often show sex reversal, i.e., develop as XY females. It has been documented that C57BL mice with the Y chromosome from Poschiavinus (YPOS), a domesticus subtype, always develop as females or hermaphrodites. This suggests that a C57BL gene either up- or downstream of Sry is ineffective in interacting with Sry, which then compromises the processes that lead to normal male sex development. Nonetheless, by selective breeding, we have been able to generate a sex reversal-resistant C57BL/6-congenic strain of mice in which the XYPOS individuals consistently develop as normal males with bilateral testes. Because the resistance to sex reversal was transferred from strain 129S1/Sv (nonalbino) by simple selection over 13 backcross generations, it is inferred that a single autosomal gene or chromosomal region confers resistance to the sex reversal that would otherwise result. XYPOS normal males generated in these crosses were compared to XYPOS abnormal individuals and to C57BL/6 controls for sexual phenotype, gonadal weight, serum testosterone, and major urinary protein (MUP) level. A clear correlation was found among phenotypic sex, MUP level, and testis weight in the males and in the incompletely masculinized XYPOS mice. The fully masculinized males of the congenic strain resemble C57BL/6 males in the tested parameters. DNA analysis confirmed that these males, in fact, carry the YPOS Sry gene.

Alpha-Globulins↗

PubMed2000

Receptor-specific influence of endothelin-1 in the erectile response of the rat.

Specific receptor antagonists were used to examine the role of endothelin-1 (ET-1) in the erectile response of the rat. In these studies, intact rats were cannulated to permit the continuous recording of mean arterial pressure (MAP) and intracavernosal pressure (CCP). Erection was induced by electrical stimulation of the autonomic ganglion, which regulates blood flow to the penis. The animals were subjected to intracavernosal injection with vehicle only (Cont) or with an antagonist to the endothelin-A receptor (ET(A)) or to the endothelin-B receptor (ET(B)). Blockade of the ET(A) or the ET(B) had no effect on the erectile response (CCP/MAP) during maximal ganglionic stimulation. When ET-1 was injected into Cont rats, there was a marked vasoconstriction with a sharp rise in MAP and a decline in CCP as the cavernosal arterioles constricted and limited inflow. The injection of the ET(A) antagonist prevented the vasoconstriction after ET-1 injection into Cont rats, whereas blockade of the ET(B) had no effect on the vasoconstrictive effect to ET-1. Similar results were obtained during submaximal ganglionic stimulation. With minimal levels of ganglionic stimulation, ET-1 injection led to a moderated degree of vasodilation in the presence of the ET(A) antagonist. The ET(B) antagonist failed to alter the CCP response during minimal stimulation, but it did have a marked effect on the MAP response to ET-1 injection. The results of these studies confirm that cavernosal tissue of the rat penis is highly responsive to ET-1. However, the failure of the ET-1 antagonists to affect penile erection in response to ganglionic stimulation reflects a minimal role of ET-1 in the erectile response in the rat.

Animals↗

PubMed1999

Androgenic maintenance of the erectile response in the rat.

Ongoing studies in this laboratory have used the castrated rat, with and without testosterone replacement, to investigate how androgens maintain the erectile response. The high intracavernosal pressures during erection depend on both an increase in the rate at which blood flows into the sinuses of the corpus cavernosum and a decrease in the rate at which blood flows out (veno-occlusion). Accordingly, our studies investigated androgenic regulation of the arterioles that regulate inflow and of the intracavernosal muscle that regulates the veno-occlusive mechanism controlling outflow. The results of these studies show that castration causes a decline in the rate of inflow and that androgen replacement reverses this decline. The decline in inflow in the castrated rats is also reversed by the administration of a nitric oxide donor drug, suggesting that the androgen may regulate inflow by increasing the synthesis of nitric oxide. Testosterone also appears to regulate outflow by controlling the sensitivity of the erectile mechanisms to norepinephrine, considered to be the principle vaso-constrictor neurotransmitter in the erectile response. Taken together, the results of these studies suggest that androgens control the erectile response by altering the synthesis and action of the neurotransmitters that normally alter the state of contraction and relaxation of smooth muscle in the erectile tissue.

Androgens↗