Purinergic neurotransmission to the fibromuscular stroma of the guinea-pig and mouse prostate gland.

The aims of this thesis were to (1) examine the effects of exogenous purines on prostate contractility in the guinea-pig prostate, (2) determine the role of adenosine receptors in regulating prostatic smooth muscle tone in this species, (3) investigate the ability of several P2X1 receptor antagonists to inhibit the purinergic component of contractile responses of the guinea-pig prostate and therefore their suitability for experimental and/ or therapeutic use, (4) develop an age-related proftle of purinergic signalling in the guinea-pig prostate to reveal dynamic function with increasing age and its possible involvement in the contractile pathology of benign prostatic hyperplasia and (5) use P2Xl receptor knockout mice to clarify the role of this receptor in prostate contractility. Chapter 3 investigated whether adenosine modulates neurotransmission as it has been shown to do in other visceral and vascular smooth muscle preparations. In contrast to other studies, adenosine exerted no neuromodulatory effect on neurogenic contractions within the prostate of this species. Further functional studies using exogenously administered pyrimidines revealed that UTP and UDP are not involved in evoking contractile responses in unstimulated tissues, nor were they found to modulate contractile responses to neurogenic stimulation. Ammonium salt forms of ADP potentiated contractile responses to electrical field stimulation and exogenous noradrenaline in the guinea-pig prostate. Experiments determined that the ammonium and not ADP was the physiologically active constituent of the compound responsible for these excitatory effects. Consistent with the findings of other studies, noradrenaline significantly potentiated responses to exogenously administered A TP, presumably via Ca2 + sensitisation. Given the paucity of selective agonists and antagonists in the field of purinergic signalling for the characterisation of purinergic responses, chapter 4 tested the purinergic antagonists NF449, TNP-ATP and RO-1 to determine whether they were effective in blocking P2Xl receptor-mediated contractility in the prostate. NF449 was far superior to TNP-ATP, RO-1, (X~methylene ATP and suramin in attenuating the non-adrenergic component of the neurogenic contraction in the guinea-pig prostate. Furthermore, NF449 defined the extent of the purinergic component of contraction, indicating that as in other studies, purinergic signalling predominates at lower frequency stimulation and is responsible for the rapid upstroke of force rather than the slower sustained portion of the contraction. Purinergic signalling is renowned for its plasticity in the control of physiologic and pathophysiologic processes that occur with growth, development and ageing. Chapter 5 aimed to characterize the age-related changes which occur to neurotransmission and prostate contractility in the guinea-pig. When adjusted for tissue weight, responses to electrical field stimulation and the administration of exogenous adrenergic and purinergic agonists were greater in prostates taken from prepubertal guinea-pigs than prostates taken from postpubertal or mature guinea-pigs. Given the lack of effective and selective purinergic receptor antagonists as described in chapter 4, chapter 6 investigated neurotransmission and smooth muscle contractility in prostates using tissue taken from genetically modified P2Xl receptor knockout mice. Mouse prostate but not body or vas deferens weight was significantly reduced in P2Xl receptor deficient mice. Maximum responses evoked by purinergic agonists were much smaller compared to those reported for adrenergic agonists in the literature. A concomitant reduction in purinergic agonist potency and contractility was also exhibited between genotypes associated with the loss of the P2Xl receptor. This confirms the presence of functional P2Xl receptors in the wild-type mouse prostate. In contrast to the vas deferens, selective blockade or deletion of the P2Xl receptor had no effect on contractile responses to electrical field stimulation between genotypes, indicating that A TP is not the principal neurotransmitter responsible for the residual non-adrenergic component of contraction in the mouse prostate. Chapter 7 presents concluding remarks which indicate that this body of work is clinically significant in that P2Xl receptors may represent an alternate or additional therapeutic target for benign prostatic hyperplasia. The limitations and possible future directions of this research are also discussed. \’