what is necessary for filling SysCache?

Hello

I added two new columns to pg_proc. I have a problem because access
via SearchSysCache doesn't work

/* Search syscache by name only */
catlist = SearchSysCacheList(PROCNAMEARGSNSP, 1,

CStringGetDatum(funcname),
0, 0, 0);

for (i = 0; i < catlist->n_members; i++)
{
HeapTuple proctup = &catlist->members[i]->tuple;
Form_pg_proc procform = (Form_pg_proc) GETSTRUCT(proctup);

...
elog(NOTICE, "%d", SysCacheGetAttr(PROCOID, proctup,
Anum_pg_proc_prondefargs, &isnull));
elog(NOTICE, "%d %d", procform->prondefargs, procform->pronargs);

result:

postgres=# select fo(10,20);
NOTICE: 1
NOTICE: 0 1
NOTICE: 2
NOTICE: 0 2
NOTICE: 2
NOTICE: 0 3
fo
----
10
(1 row)

what is mechanism, that select between directly accessed fields and
fields that are accessed via SysCacheGetAttr?

Thank you
Pavel Stehule