Urination after masturbation.

Sexual arousal and stimulation causes the bladder to fill.

Renal output is highly variable, and when the sympathetic nervous system is not at baseline, other agents besides antidiuretic hormone (vasopressin) become dominant in renal output regulation. One of these is a cardiac peptide called atrial natriuretic peptide (ANP). Initially, sexual arousal is a highly parasympathetic state that involves the use of these cardiac peptides as powerful vasodilator. The kidneys have receptors for ANP, and they cause a large increase in glomerular pressure, which increases renal output. Renal output can be on average as high as 10ml/min under certain conditions. So even when you pee before, you may need to go again after.
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I have experienced it. Also I urinate a lot more in sense of time. I remember back when I was wanking all day all night the next day my dick used to be so sore that I felt the pain while peeing and I had to pee every hour. That was horrible and unbearable pain. But my stupid ass overlooked it and kept on with pmo. Glad it is all stopped now.

 

I felt the same way.

 

Yes, peeing when you are erect is tricky. I assume it is because the body is in readiness to cum, so the bladder is kind of locked off from emptying into the urethra (tube that comes out of your dick). Probably a sphincter muscle does this, but I am not that knowledgeable about biology either (@R.I.I.P.E.R's post is over the heads of most people here I should think).

 

Hmm, it is an interesting question. It has not occurred to me before, but I think the answer might be yes(?). It is a little more difficult to say for sure in my case because I am diabetic, so I can need to pee a bit more anyway. Not sure, lol.

Yeah, I can definitely relate to your experience @Grow_out_of_it. I got it into my dumb ass brain when I was a teenager that I could get the ultimate pleasure from jerking off as orgasm approached, by doing it as fast as possible and with a vice-like death grip! There is no logic to it really because these things don't replicate intercourse! But, yeah, I used to get pain in the urethra and it was painful to piss. I am not sure whether it was crushed from the death grip, or if the violent jerking off caused some micro tears or abrasions to it. It was a stinging pain! But, like you, I carried on masturbating!

 

I just assume that it's the body clearing out the plumbing.