Sex: A Horizon Guide Page #3

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The solution came in the form

of a chemical compound

developed in the late '90s.

Scientists at Pfizer were

looking for a new drug for angina,

something that would relax

the blood vessels around the heart.

After screening

hundreds of thousands of compounds,

they ended up with UK-92,480.

But its trials in humans

were a letdown.

It was about to be consigned

back to the stores

when the triallists came back

reporting an unusual side effect -

lots of erections.

Add the drug, and the relaxations

get larger.

But it's... The trace's upside down.

By making a crude mock-up

of the human sexual apparatus,

senior scientist Chris Wayman

found an ingenious way

to test this anecdotal evidence.

These are actually

penile blood vessels

that we have in a tissue bath.

Think of this as the brain, this is

the brain and the spinal cord.

When you become aroused,

your brain switches on.

We can mimic this

by switching on the equivalent of the

central nervous system in the brain.

It sends electricity down to the

tissue baths and across the tissues.

And when we pass an electric current

across these small pieces

of penile tissue, they relax,

and ultimately that's what happens

during penile erection.

Relaxed penile blood vessels

mean more blood flow to the penis,

and so an erection.

What Chris did was take penile

blood vessels from impotent men,

vessels that didn't respond

when he flipped the brain-switch,

and then added UK-92,480

to the tissue bath.

What was most amazing

about this study

was that we saw a restoration of

erectile response.

It's very rare

in any tissue preparation

to convert dysfunctional

to normal function.

So now we were onto something that

can only be described as special.

UK-92,480 was renamed Viagra.

And within weeks of going on sale,

tens of thousands of prescriptions

were being written every day.

You would never have been able

to predict

that this was going to

have beneficial effects

on millions and millions of men

throughout the world.

A little bit of science having

an effect of self-esteem, anxiety,

depression levels and ultimately

creating enhanced relationships.

Today, Viagra is one of

the most widely prescribed drugs

in the world, with about six tablets

being dispensed every second.

By fumbling in the dark,

science had fixed a problem

that had plagued men for centuries.

But there are bigger

and deadlier problems

when it comes to sex,

and some of them would prove

much more resistant

to scientific solutions.

Sex brings bodies into intimate

physical contact with each other.

But it also allows sexually

transmitted diseases to travel

from one person to another.

But by the 1970s many of these

diseases were under control -

in the developed world at least.

Then, in the early 1980s, along came

a terrifying new sexual infection.

Horizon broadcast

one of the first documentaries

about this terrible new disease.

The first troubling signs

were noticed

in the homosexual communities

of America,

in particular in

New York's Greenwich Village.

Gay men were contracting

bizarre infections

that seldom infected healthy people.

Toxoplasmosis,

Pneumocystis carinii pneumonia,

Cryptosporidiosis,

and types of tuberculosis

that normally only infected birds

were killing men in their prime.

Then the disease was noticed

in intravenous drug users,

many of who were in prison by the

time they started having symptoms.

Prisoner Castranova's speech

is affected.

He may have Toxoplasmosis

as well as the pneumonia.

This is one of his better days.

What's rough now is,

I don't know

if I'll ever see my kids again.

Scientists were horrified

when they looked at blood

taken from these patients.

The numbers of a particular

white blood cell,

known as a T helper cell,

were at rock bottom.

Without this vital cornerstone

of the immune system,

infections which would normally be

easily fended off

could become lethal.

Finally, behind all these

odd infections,

scientists discovered

a puppet master.

Something that was weakening

the immune system,

allowing other, usually mild,

infections to wreak havoc.

They tracked down the cause

of what had become known as acquired

immunodeficiency syndrome - AIDS.

It was a virus - HIV.

Like a walking time bomb.

You know?

That's what they said.

"You're like a walking time bomb."

He died soon after.

And Mrs Castranova also died.

She was incubating AIDS

while her husband was in prison.

Since HIV was first identified,

over 60 million people have become

infected worldwide.

Of those who contracted the virus,

AIDS has killed 30 million people.

It's one of the worst pandemics

the world has ever known.

In the intervening years,

science has scrambled to find drugs

that could cure the disease,

with only limited success.

COCKEREL CROWS:

But then something surprising

was noticed

in a valley in Central Africa.

Something which would suggest

an effective way

of combating the disease.

On one side of the valley people

are dying of AIDS in their hundreds,

while their neighbours, with the same

apparent behaviour and risk,

are far less affected by the disease.

MAN SPEAKS IN OWN LANGUAGE

In this school, if the epidemic

continues to spread,

60% of these children

will die from AIDS.

But the extraordinary thing is

that if they were children

just a mile away

on the other side of this valley,

their chances of dying

would be three times less.

Scientists realised

the only difference

between the AIDS-free side

of the valley and the other

was that the boys

on the healthy side

had been circumcised,

according to local custom.

Removing the foreskin seemed

to have an almost miraculous effect

in preventing the men

from getting infected.

Intrigued by the idea,

anthropologist Priscilla Reining

compiled data

on hundreds of circumcised

and uncircumcised tribes.

When this data was matched up

with a map of HIV prevalence,

the correlation was startling.

This was the map which we published,

and the black are depicting

ethnic groups

which do not practice circumcision

as a norm, and the grey

are groups

which do practice circumcision.

So this is a corridor which runs

from the southern Sudan

down into South Africa.

Here is an overlay of HIV.

And you can see that

there's a high degree of conformity

between the red, which is

relatively high HIV rates.

There is red

down the same band, and...

..interestingly,

over here as well.

The statistical...

statistical relationship was .90,

which is very good.

And so, you know, wow,

it really is there.

But why should circumcision

so drastically cut the risk

of HIV infection?

The answer lay in particular cells

of the immune system

present in the foreskin.

Cells which HIV was targeting.

The green cells

are Langerhans cells.

They're in the front line of

the body's battle against infection.

They capture infectious agents

like viruses

and show them to other cells

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